托福阅读TPO50文本+题目+答案+解析（含PDF下载）
托福阅读TPO50文本+题目+答案+解析（含PDF下载）
American Railroads
美国铁路
托福阅读TPO50文本：
In the United States, railroads spearheaded the second phase of the transportation revolution by overtaking the previous importance of canals. The mid-1800s saw a great expansion of American railroads. The major cities east of the Mississippi River were linked by a spiderweb of railroad tracks. Chicago's growth illustrates the impact of these rail links. In 1849 Chicago was a village of a few hundred people with virtually no rail service. By 1860 it had become a city of 100,000, served by eleven railroads. Farmers to the north and west of Chicago no longer had to ship their grain, livestock, and dairy products down the Mississippi River to New Orleans; they could now ship their products directly east. Chicago supplanted New Orleans as the interior of America's main commercial hub.
The east-west rail lines stimulated the settlement and agricultural development of the Midwest. By 1860 Illinois, Indiana, and Wisconsin had replaced Ohio, Pennsylvania, and New York as the leading wheat-growing states. Enabling farmers to speed their products to the East, railroads increased the value of farmland and promoted additional settlement. In turn, population growth in agricultural areas triggered industrial development in cities such as Chicago, Davenport (Iowa), and Minneapolis, for the new settlers needed lumber for fences and houses and mills to grind wheat into flour.
Railroads also propelled the growth of small towns along their routes. The Illinois Central Railroad, which had more track than any other railroad in 1855, made money not only from its traffic but also from real estate speculation. Purchasing land for stations along its path, the Illinois Central then laid out towns around the stations. The selection of Manteno, Illinois, as a stop of the Illinois Central, for example, transformed the site from a crossroads without a single house in 1854 into a bustling town of nearly a thousand in 1860, replete with hotels, lumberyards, grain elevators, and gristmills. By the Civil War (1861-1865), few thought of the railroad-linked Midwest as a frontier region or viewed its inhabitants as pioneers.
As the nation's first big business, the railroads transformed the conduct of business. During the early 1830s, railroads, like canals, depended on financial aid from state governments. With the onset of economic depression in the late 1830s, however, state governments scrapped overly ambitious railroad projects. Convinced that railroads burdened them with high taxes and blasted hopes, voters turned against state aid, and in the early 1840s, several states amended their constitutions to bar state funding for railroads and canals. The federal government took up some of the slack, but federal aid did not provide a major stimulus to railroads before 1860. Rather, part of the burden of finance passed to city and county governments in agricultural areas that wanted to attract railroads. Such municipal governments, for example, often gave railroads rights-of-way, grants of land for stations, and public funds.
The dramatic expansion of the railroad network in the 1850s, however, strained the financing capacity of local governments and required a turn toward private investment, which had never been absent from the picture. Well aware of the economic benefits of railroads, individuals living near them had long purchased railroad stock issued by governments and had directly bought stock in railroads, often paying by contributing their labor to building the railroads. But the large railroads of the 1850s needed more capital than such small investors could generate. Gradually, the center of railroad financing shifted to New York City, and in fact, it was the railroad boom of the 1850s that helped make Wall Street in New York City the nation's greatest capital market. The stocks of all the leading railroads were traded on the floor of the New York Stock Exchange during the 1850s. In addition, the growth of railroads turned New York City into the center of modern investment firms. The investment firms evaluated the stock of railroads in the smaller American cities and then found purchasers for these stocks in New York City, Philadelphia, Paris, London, Amsterdam, and Hamburg. Controlling the flow of funds to railroads, the investment bankers began to exert influence over the railroads' internal affairs by supervising administrative reorganizations in times of trouble.
篇：托福阅读TPO50题目：
Question 1 of 14
According to paragraph 1, what effect did the expansion of rail links have on Chicago?
A. Chicago became the headquarters for eleven new railroads.
B. Chicago became the most important city east of the Mississippi River.
C. Chicago was transformed from a village into a large city.
D. Chicago replaced eastern cities as the main buyer of farm products from the region.
Question 2 of 14
Paragraph 2 supports the idea that Illinois, Indiana, and Wisconsin were able to become the leading wheat-growing states by 1860 in large part because
A. by 1860 there were more railroads in Illinois, Indiana, and Wisconsin than in Ohio, Pennsylvania, and New York.
B. the expansion of east-west rail lines made transporting Midwestern products to East Coast markets relatively fast and easy.
C. by 1860 states such as Ohio, Pennsylvania, and New York had become more interested in industrial development than in agriculture.
D. most of the farmers who had grown wheat in Ohio, Pennsylvania, or New York resettled in the Midwest after the expansion of east-west rail lines.
Question 3 of 14
The word "promoted" in the passage is closest in meaning to
A. encouraged.
B. controlled.
C. promised.
D. predicted.
Question 4 of 14
According to paragraph 2, one effect of the increased agricultural development in the Midwest was to
A. slow the rate at which population grew in many Midwestern cities.
B. increase the demand for industrial products from Midwestern cities.
C. encourage the extension of east-west rail lines to the Midwest.
D. reduce the pressure on Midwestern farmers to get their products to market faster.
Question 5 of 14
The author mentions "Manteno, Illinois" in order to
A. give an example of how railroads decided which small towns would be selected for stations.
B. illustrate the power of railroads to determine where towns would come into existence.
C. explain how some railroads were able to make more money from real estate speculation than from railroad traffic.
D. show how people's view of the Midwest as a frontier region had changed by the Civil War.
Question 6 of 14
The word "bustling" in the passage is closest in meaning to
A. commercial.
B. wealthy.
C. lively.
D. modern.
Question 7 of 14
The word "onset" in the passage is closest in meaning to
A. possibility.
B. fear.
C. worsening.
D. start.
Question 8 of 14
According to paragraph 4, how were railroads affected by the economic depression in the late 1830s?
A. They lost important funding from state governments.
B. They began to realize that some of their projects were overly ambitious.
C. They had to compete with canals for government support.
D. They emerged as the nation's biggest business.
Question 9 of 14
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. Private investment in railroads began in the 1850s following the dramatic expansion of the railroad network, which had been financed by local governments.
B. Railroads' relations with local governments became strained in the 1850s, when railroads turned to private investors for financing to expand their capacity.
C. Local governments' limited capacity to finance railroad expansion was a long-standing problem that railroads solved in the 1850s by turning toward private investment.
D. When local governments could not adequately finance the railroads' dramatic expansion in the 1850s, private investment became increasingly important.
Question 10 of 14
Paragraph 5 supports which of the following ideas about people who held railroad stock?
A. Many of them were not particularly wealthy.
B. Many of them overestimated the economic benefits of railroads.
C. Most of them bought their stock for less than it was worth.
D. Most of them had been employed by a railroad.
Question 11 of 14
According to paragraph 5, investment bankers were involved in all of the following EXCEPT
A. controlling the distribution of funds to railroads.
B. finding national and international buyers of railroad stock.
C. overseeing administrative changes of railroads when needed.
D. persuading the federal government to reinvest in railroads.
Question 12 of 14
The word "flow" in the passage is closest in meaning to
A. promise.
B. growth.
C. movement.
D. source.
Question 13 of 14
Look at the four squares [[span class='strong-insert']][[/span]] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? Click on a square [[span class='strong-insert']][[/span]] to add the sentence to the passage .
Indeed, the network became so dense that by the 1860s the United States had more miles of railroad tracks than did all the rest of the world.
Question 14 of 14
Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it To review the passage, click VIEW TEXT. The expansion of railroads in the mid-1800s played an important role in the development of the American Midwest .
A.Increased rail line between the East and the Midwest resulted in the rapid rise of major Midwestern cities such as Chicago, as well as in the growth of small towns along railroad routes.
B.Real estate speculation by railroads in the 1850s drove up the value of farmland and encouraged many Midwestern farmers to sell their land and make a new life in the cities.
C.Both canals and railroads fell out of public favor in the early 1840s, but by the mid-1850s the economic benefits of railroads had once again become generally recognized.
D.Once Chicago became a major commercial hub with direct rail connections to New Orleans and the East, Midwestern farmers were no longer limited to selling most of their products locally.
E.State government financing of railroads largely ended in the 1830s and was replaced by a combination of local and federal government support and money from private investors.
F.In the 1850s railroads turned to investment banks in New York City for capital to expand and by doing so, helped establish the city as the main financial center in the United States.
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The Achievement of Brazilian Independence
巴西独立的实现
In contrast to the political anarchy, economic dislocation, and military destruction in Spanish America, Brazil's drive toward independence from Portugal proceeded as a relatively bloodless transition between 1808 and 1822. The idea of Brazilian independence first arose in the late eighteenth century as a Brazilian reaction to the Portuguese policy of tightening political and economic control over the colony in the interests of the mother country. The first significant conspiracy against Portuguese rule was organized from 1788-1799 in the province of Minas Gerais, where rigid governmental control over the production and prices of gold and diamonds, as well as heavy taxes, caused much discontent. But this conspiracy never went beyond the stage of discussion and was easily discovered and crushed. Other conspiracies in the late eighteenth century as well as a brief revolt in 1817 reflected the influence of republican ideas over sections of the elite and even the lower strata of urban society. All proved abortive or were soon crushed. Were it not for an accident of European history, the independence of Brazil might have been long delayed.
The French invasion of Portugal in 1807 followed by the flight of the Portuguese court (sovereign and government officers) to Rio de Janeiro brought large benefits to Brazil. Indeed, the transfer of the court in effect signified achievement of Brazilian independence. The Portuguese prince and future King Joao VI opened Brazil's ports to the trade of friendly nations, permitted the rise of local industries, and founded the Bank of Brazil. In 1815 he elevated Brazil to the legal status of a kingdom coequal with Portugal. ln one sense, however, Brazil's new status signified the substitution of one dependence for another. Freed from Portuguese control, Brazil came under the economic dominance of England, which obtained major tariff concessions and other privileges by the Strangford Treaty of 1810 between Portugal and Great Britain. The treaty provided for the importation of British manufactures into Brazil and the export of Brazilian agricultural produce to Great Britain. One result was an influx of cheap machine-made goods that swamped the handicrafts industry of the country.
Brazilian elites took satisfaction in Brazil's new role and the growth of educational, cultural, and economic opportunities for their class. But the feeling was mixed with resentment toward the thousands of Portuguese courtiers (officials) and hangers-on who came with the court and who competed with Brazilians for jobs and favors. Thus, the change in the status of Brazil sharpened the conflict between Portuguese elites born in Brazil and elites born in Portugal and loyal to the Portuguese crown.
The event that precipitated the break with the mother country was the revolution of 1820 in Portugal. The Portuguese revolutionaries framed a liberal constitution for the kingdom, but they were conservative or reactionary in relation to Brazil. They demanded the immediate return of King Joao to Lisbon, an end to the system of dual monarchy that he had devised, and the restoration of the Portuguese commercial monopoly. Timid and vacillating, King Joao did not know which way to turn. Under the pressure of his courtiers, who hungered to return to Portugal and their lost estates, he finally approved the new constitution and sailed for Portugal. He left behind him, however, his son and heir, Pedro, and in a private letter advised him that in the event the Brazilians should demand independence, he should assume leadership of the movement and set the crown of Brazil on his head.
Soon it became clear that the Portuguese parliament intended to set the clock back by abrogating all the liberties and concessions won by Brazil since 1808. One of its decrees insisted on the immediate return of Pedro from Brazil. The pace of events moved more rapidly in 1822. On January 9, urged on by Brazilian advisers who perceived a golden opportunity to make an orderly transition to independence without the intervention of the masses, Pedro refused an order from the parliament to return to Portugal, saying famously, "l remain." On September 7, regarded by all Brazilians as Independence Day, he issued the even more celebrated proclamation, "Independence or death!" In December 1822, having overcome slight resistance by Portuguese troops, Dom Pedro was formally proclaimed constitutional Emperor of Brazil.
第二篇：托福阅读TPO50题目：
Question 1 of 14
The word "anarchy" in the passage is closest in meaning to
A. uncertainty.
B. disorder.
C. powerlessness.
D. violence.
Question 2 of 14
According to paragraph 1, what first caused Brazilians to think seriously about trying to achieve independence from Portugal?A. Portugal's declining interest in having overseas colonies.
B. Portugal's moves to gain political and economic control of Brazil for its own advantage.
C. The drive toward independence going on at the time in parts of Spanish America.
D. The Portuguese reaction to Brazil's efforts to gain control over its economy.
Question 3 of 14
According to paragraph 1, what happened to the 1788-1799 conspiracy against Portuguese rule?
A. It ended up creating discontent in certain provinces of Brazil.
B. It increasingly came under the influence of republican ideas from Portugal.
C. It was crushed before it got beyond the planning stage.
D. It gradually lost the support of the lower strata of urban society.
Question 4 of 14
According to paragraph 2, Brazil gained a significant measure of independence early in the nineteenth century primarily as a result of
A. the Portuguese prince's desire to become King of Brazil rather than King of Portugal.
B. Brazil's growing industrial and financial importance.
C. the flight of the Portuguese court to Rio de Janeiro.
D. the Strangford Treaty with England.
Question 5 of 14
According to paragraph 2, King Joao did each of the following for Brazil EXCEPT
A. establish a national bank.
B. support Brazilian industries.
C. obtain important tariff concessions from England.
D. encourage trade with a wider range of nations.
Question 6 of 14
The word "precipitated" in the passage is closest in meaning to
A. came before.
B. brought about.
C. resulted from.
D. slowed down.
Question 7 of 14
According to paragraph 4, the Portuguese revolutionaries insisted on each of the following EXCEPT
A. King Joao’s immediate return to Portugal.
B. the creation of a liberal constitution for Brazil.
C. an end to Brazil's status as a kingdom.
D. Portuguese control over the Brazilian economy.
Question 8 of 14
The word "Timid" in the passage is closest in meaning to
A. Fearful.
B. Angry.
C. Poor.
D. Sickly.
Question 9 of 14
In paragraph 4, why does the author mention that King Joao's courtiers "hungered to return to Portugal and their lost estates"?
A. To illustrate how conservative the courtiers were.
B. To help explain the position taken by the courtiers.
C. To give an example of the effects produced by the revolution.
D. To show why King Joao advised his son the way he did.
Question 10 of 14
Paragraphs 4 and 5 support the idea that Brazil's move to declare independence in 1822 was primarily the result of
A. the revolutionaries' demand that King Joao return to Portugal.
B. Portugal's apparent intention to return Brazil to the status of a colony.
C. King Joao's decision to leave his son Pedro in Brazil.
D. the growing threat of intervention by the Brazilian masses.
Question 11 of 14
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. On January 9, 1822, Brazil achieved independence without any involvement by the masses when Pedro, despite the urging of his Brazilian advisers, defied a parliamentary order to return to Portugal.
B. Following the urging of Brazilian advisers, on January 9, 1822, the Portuguese parliament ordered Pedro to return, but, hoping to avoid conflict with the masses, Pedro declared, "l remain.".
C. The best opportunity for Brazil to achieve independence without involving the masses came on January 9. 1822, but Pedro, saying, "I remain," refused an order to return to Portugal.
D. Seeing the possibility of an orderly transition to independence, Pedro's Brazilian advisers urged him to refuse to return to Portugal, and on January 9, 1822, Pedro did refuse, declaring, "I remain.".
Question 12 of 14
According to paragraph 5, Independence Day in Brazil is the date on which
A. Brazil made Dom Pedro its constitutional Emperor.
B. Dom Pedro refused to comply with the Portuguese parliament's demand that he return to Portugal.
C. the Portuguese parliament officially withdrew all formal connection to Brazil.
D. Dom Pedro publicly declared his position by saying, "Independence or death!".
Question 13 of 14
Look at the four squares [[span class='strong-insert']][[/span]] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? Click on a square [[span class='strong-insert']][[/span]] to add the sentence to the passage .
Therefore, although still closely linked to Portugal, Brazil was no longer formally considered a colony.
Question 14 of 14
Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. To review the passage, click VIEW TEXT. It was only after the Portuguese court moved to Brazil that significant progress toward Brazilian independence began .
A.Major conspiracies against Portuguese dominance developed in regions where governmental control over Brazil's economy had produced a spirit of revolt among Brazilian merchants.
B.King Joao effectively freed Brazil from Portugal's political and economic control and in 1815 elevated Brazil to the legal status of a kingdom coequal with Portugal.
C.After freeing itself from Portuguese control. Brazil almost immediately fell under the control of England, which used its economic power to advance Brazil's local industry for England's benefit.
D.The presence of King Joao and his court in Rio de Janeiro created competition and tension with the Portuguese elites born in Brazil, who had no loyalties to the Portuguese crown.
E.After the Portuguese revolution in 1820, Portugal attempted to reestablish complete control over Brazil; but although King Joao returned to Lisbon, Pedro, his son and heir, remained in Brazil.
F.In 1822 Dom Pedro refused Portugal's demand that he return, declared Brazil's independence, and by the year’s end had become constitutional Emperor of an independent Brazil.
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Star Death
恒星的衰亡
Until the early- to mid-twentieth century, scientists believed that stars generate energy by shrinking. As stars contracted, it was thought, they would get hotter and hotter, giving off light in the process. This could not be the primary way that stars shine, however. If it were, they would scarcely last a million years, rather than the billions of years in age that we know they are. We now know that stars are fueled by nuclear fusion. Each time fusion takes place, energy is released as a by-product.This energy, expelled into space, is what we see as starlight. The fusion process begins when two hydrogen nuclei smash together to form a particle called the deuteron (a combination of a positive proton and a neutral neutron). Deuterons readily combine with additional protons to form helium. Helium, in turn, can fuse together to form heavier elements, such as carbon. In a typical star, merger after merger takes place until significant quantities of heavy elements are built up.
We must distinguish, at this point, between two different stellar types: Population I and Population ll, the latter being much older than the former. These groups can also be distinguished by their locations. Our galaxy, the Milky Way, is shaped like a flat disk surrounding a central bulge. Whereas Population I stars are found mainly in the galactic disk, Population II stars mostly reside in the central bulge of the galaxy and in the halo surrounding this bulge.
Population II stars date to the early stages of the universe. Formed when the cosmos was filled with hydrogen and helium gases, they initially contained virtually no heavy elements. They shine until their fusible material is exhausted. When Population II stars die, their material is spread out into space. Some of this dust is eventually incorporated into newly formed Population I stars. Though Population I stars consist mostly of hydrogen and helium gas, they also contain heavy elements (heavier than helium), which comprise about 1 or 2 percent of their mass. These heavier materials are fused from the lighter elements that the stars have collected.Thus, Population I stars contain material that once belonged to stars from previous generations. The Sun is a good example of a Population I star.
What will happen when the Sun dies? In several billion years, our mother star will burn much brighter. It will expend more and more of its nuclear fuel, until little is left of its original hydrogen. Then, at some point in the far future, all nuclear reactions in the Sun’s center will cease.
Once the Sun passes into its "postnuclear" phase, it will separate effectively into two different regions: an inner zone and an outer zone. While no more hydrogen fuel will remain in the inner zone, there will be a small amount left in the outer zone. Rapidly, changes will begin to take place that will serve to tear the Sun apart. The inner zone, its nuclear fires no longer burning, will begin to collapse under the influence of its own weight and will contract into a tiny hot core, dense and dim. An opposite fate will await the outer region, a loosely held-together ball of gas. A shock wave caused by the inner zone's contraction will send ripples through the dying star, pushing the stellar exterior's material farther and farther outward. The outer envelope will then grow rapidly, increasing, in a short interval, hundreds of times in size. As it expands, it will cool down by thousands of degrees. Eventually, the Sun will become a red giant star, cool and bright. It will be so large that it will occupy the whole space that used to be the Earth's orbit and so brilliant that it would be able to be seen with the naked eye thousands of light-years away. It will exist that way for millions of years, gradually releasing the material of its outer envelope into space. Finally, nothing will be left of the gaseous exterior of the Sun; all that will remain will be the hot, white core. The Sun will have become a white dwarf star. The core will shrink, giving off the last of its energy, and the Sun will finally die.
第三篇：托福阅读TPO50题目：
Question 1 of 14
The word "readily" in the passage is closest in meaning to
A. eventually.
B. easily.
C. constantly.
D. loosely.
Question 2 of 14
According to paragraph 1, the energy that comes from stars and that is seen as light is the result of
A. protons combining with helium atoms.
B. atoms of heavier elements smashing together.
C. various particles fusing with one another.
D. hydrogen atoms breaking apart.
Question 3 of 14
In paragraph 1, why does the author point out that stars are billions of years old?
A. To establish that starlight is produced by an ongoing process and not by a one-time event.
B. To suggest that stars contract much more slowly than was previously believed.
C. To argue that shrinking cannot be the main way stars generate energy.
D. To argue that fusion in a star slows down as quantities of heavy elements build up.
Question 4 of 14
According to paragraph 2, Population I stars and Population II stars differ from each other in terms of both
A. how old they are and where in their galaxies they are found.
B. how old they are and whether they have a halo around them.
C. where in their galaxies they are found and whether they bulge out in the center.
D. whether they are at the center of a flat disk and whether they have a halo.
Question 5 of 14
According to paragraphs 2 and 3, all of the following are true of Population I stars EXCEPT
A. They contain material that was once contained in Population II stars.
B. In terms of their mass, they consist primarily of hydrogen and helium.
C. They contain elements that were formed through the fusion of lighter ones.
D. They generally do not last as long as Population II stars.
Question 6 of 14
The word "virtually" in the passage is closest in meaning to
A. absolutely.
B. usually.
C. almost.
D. as a result.
Question 7 of 14
The word "exhausted" in the passage is closest in meaning to
A. used up.
B. released.
C. invisible.
D. broken up.
Question 8 of 14
The word "comprise" in the passage is closest in meaning to
A. absorb.
B. lose.
C. increase to.
D. make up.
Question 9 of 14
Why does the author ask the question "What will happen when the Sun dies?" ?
A. To identify the most serious question concerning star death that scientists must address.
B. To introduce the topic that the rest of the passage will discuss.
C. To suggest that scientists remain uncertain about some aspects of star death.
D. To suggest that the Sun may not be a good example of a Population I star.
Question 10 of 14
According to paragraph 5, once the Sun is in its "postnuclear" phase, the outer zone will differ from the inner zone in that the outer zone will
A. undergo a much less dramatic change in size.
B. maintain more nearly constant temperatures.
C. cease to be a site of energy-generating activity.
D. still contain some amount of hydrogen.
Question 11 of 14
According to paragraph 5, which of the following will be true about the inner core of the dying Sun?
A. It will contract, sending an energy wave through the rest of the star.
B. It will shine with a bright red glow before it finally shrinks and dies.
C. It will expand to hundreds of times its previous size.
D. It will shrink due to the weight of the outer envelope.
Question 12 of 14
Paragraph 5 supports which of the following about the death of the Sun?
A. The Sun's outer envelope will expand rapidly as a result of decreasing temperatures in the outer zone.
B. The Sun will reach the red giant stage millions of years before it becomes a white dwarf star.
C. After the Sun has released the material of its outer envelope into space, nuclear fusion will continue at the remaining core for a limited period.
D. While the outer region of the Sun expands, it releases all its material into space.
Question 13 of 14
Look at the four squares [[span class='strong-insert']][[/span]] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? Click on a square [[span class='strong-insert']][[/span]] to add the sentence to the passage .
Clearly, a more plausible mechanism was needed to explain how stars generate energy.
Question 14 of 14
Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. To review the passage, click VIEW TEXT. Stars generate the energy that makes them shine as a by-product of nuclear fusion and not by shrinking, as scientists had once believed .
A.The Sun is a good example of a Population I star because the Sun generates its energy through nuclear fusion rather than through contraction.
B.In the Milky Way, Population I stars are found in and around the central bulge and Population II stars are found in the galactic disk.
C.The Sun and stars like it will separate into inner cores and outer envelopes before all nuclear reactions in the cores stop and the stars finally die.
D.Population II stars, the oldest stars, are formed from hydrogen and helium gases, and they shine until they exhaust their fusible material.
E.Population I stars, including the Sun, are relatively young stars that are mostly hydrogen and helium gas but also contain heavier elements.
F.The outer envelope of the Sun and stars like it will release their energy into space, and the inner cores will become white dwarfs before they finally give off their last energy.
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