托福阅读常考话题及练习题推荐二：冰川（3）

► Paragraph 5： Throughout most of Earth’s history, glaciers did not exist, but at the present time about 10 percent of Earth’s land surface is covered by glaciers. Present-day glaciers are found in Antarctica, in Greenland, and at high elevations on all the continents except Australia. In the recent past, from about 2.4 million to about 10,000 years ago, nearly a third of Earth’s land area was periodically covered by ice thousands of meters thick. In the much more distant past, other ice ages have occurred.

12. According to paragraph 5, in what way is the present time unusual in the history of Earth?

A. There are glaciers.

B. More land is covered by glaciers than at anytime in the past.

C. There is no ice age.

D. No glaciers are found in Australia.

► Paragraph 1：Glaciers are slowly moving masses of ice that have accumulated on land in areas where more snowfalls during a year than melts. Snow falls as hexagonal crystals, but once on the ground, snow is soon transformed into a compacted mass of smaller, rounded grains. ■As the air space around them is lessened by compaction and melting, the grains become denser. ■With further melting, refreezing, and increased weight from newer snowfall above, the snow reaches a granular recrystallized stage intermediate between flakes and ice known as firn. ■With additional time, pressure, and refrozen meltwater from above, the small firn granules become larger, interlocked crystals of blue glacial ice. ■When the ice is thick enough, usually over 30 meters, the weight of the snow and firn will cause the ice crystals toward the bottom to become plastic and to flow outward or downward from the area of snow accumulation.

13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?

Firn has the appearance of wet sugar, but it is almost as hard as ice.

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.

Glaciers are part of Earth's hydrologic cycle.

Answer Choices

A. Glaciers, which at present contain 80 percent of Earth's freshwater, form when accumulated snow is compressed and recrystallized into ice over a period of years.

B. When there are glaciers on Earth, water is cycled through the glacier system, but the cycle period may be hundreds of thousands of years during periods of ice ages.

C. The glacial system is governed by precipitation and temperature in such a way that glaciers cannot form in temperate latitudes.

D. When glacial ice reaches a depth of 30 meters, the weight of the ice causes ice crystals at the bottom to flow, and the resulting movement of the glacier carves the landscape.

E. If global warming melted the world's glaciers, sea level would rise about 60 meters worldwide.

F. Glaciers have had little effect on Earth's surface because only 2 percent of Earth's water is currently contained in glaciers, and there are fewer glaciers now than at most times in the past.

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