Despite its effectiveness, the use of animal manure in the United States has decreased. There are three reasons for this: the replacement of most mixed animal-raising and crop-farming operations with separate operations for growing crops and raising animals, the high costs of transporting animal manure from feedlots near urban areas to distant rural crop-growing areas, and the replacement of horses and other draft animals that added manure to the soil with tractors and other motorized farm machinery.
According to paragraph 2, all of the following contributed to the decrease in the use of animal manure in the United States EXCEPT
¡ changes in crop-farming and animal-raising operations
¡ high transportation costs
¡ the movement or large numbers of feedlots to distant rural areas
¡ the introduction of motorized farm machinery
Green manure is fresh or growing green vegetation plowed into the soil to increase the organic matter and humus (degraded organic matter) available to the next crop. Compost is a sweet-smelling, dark-brown, humuslike material that is rich in organic matter and soil nutrients. It is produced when microorganisms in soil (mostly fungi and aerobic bacteria) break down organic matter such as leaves, food wastes, paper, and wood in the presence of oxygen. Compost is a rich natural fertilizer and soil conditioner that aerates soil, improves its ability to retain water and nutrients, helps prevent erosion, and prevents nutrients from being wasted by being dumped in landfills. Compost is produced by piling up alternating layers of nitrogen-rich wastes (such as grass clippings, weeds, animal manure, and vegetable kitchen scraps), carbon-rich plant wastes (dead leaves, hay, straw, sawdust), and topsoil. Compost provides a home for microorganisms that help decompose plant and manure layers and reduces the amount of plant wastes taken to landfills and incinerators.
According to paragraph 3, what is one advantage of using compost in raising crops?
¡ It makes the soil easier to plow in preparation for planting.
¡ Water and nutrients stay in the soil and enable plant growth.
¡ The damage to soil from microorganisms is reduced.
¡ Excess oxygen is removed from the soil.
Compost is a rich natural fertilizer and soil conditioner that aerates soil, improves its ability to retain water and nutrients, helps prevent erosion, and prevents nutrients from being wasted by being dumped in landfills.
此句中有几个表示正向因果动词，比如： improve, help, prevent 。这几个词也可以看作是一种正向结果关系。因此我们只要从选项中选出符合这些动词后面的优点即可。
According to paragraph 3, one important physical effect of compost is that it
¡ adds an oxygen-rich layer to the layers rich in nitrogen and carbon
¡ decreases the quantity of plant material that needs to be discarded
¡ helps keep the same amount of moisture in each layer of soil
¡ reduces the amount of fungi and aerobic bacteria in the pile
Compost provides a home for microorganisms that help decompose plant and manure layers and reduces the amount of plant wastes taken to landfills and incinerators.
这句话中我们可以注意到有两个关键性的词：help 和reduce 。主要告诉我们compost有两个结果，一是帮助分解植物和化肥层;二是减少植物肥料进入垃圾填埋区和焚化炉的数量。 由此此题应该选择c。
Corn, tobacco, and cotton can deplete the topsoil of nutrients, especially nitrogen, if planted on the same land several years in a row. One way to reduce such losses is crop rotation. Farmers plant areas or strips with nutrient-depleting crops one year. In the next year they plant the same areas with legumes, whose root nodules add nitrogen to the soil. In addition to helping restore soil nutrients, this method reduces erosion by keeping the soil covered with vegetation and helps reduce crop losses to insects by presenting them with a changing target.
According to paragraph 5, one of the main reasons for using legumes in crop rotation is that legumes
¡ have no serious insect pests
¡ cover the soil more completely than any other crop does
¡ build up the nitrogen content of the soil
¡ are very easy to plant in strips
我们仔细观察一下这道题，注意一个词组one of the main reasons 也就是说题目要求我们寻找其中的一个主要原因。那么我们来做一下预判，既然要在这个段落中寻找其中一个主要原因，那么必然原因不止一个，至少有2个原因。
In addition to helping restore soil nutrients, this method reduces erosion by keeping the soil covered with vegetation and helps reduce crop losses to insects by presenting them with a changing target.
在这句话中，我们注意到有一个表示并列关系词组：in addition to 表示这句话中有两个原因，一个是帮助储存土壤营养，一个是减少侵蚀和帮助减少因为虫害导致的农作物损失。而这个储存土壤营养其实就是前一句的氮，此题选C
Today, many farmers rely on commercial inorganic fertilizers containing nitrogen (as ammonium ions, nitrate ions, or urea), phosphorus (as phosphate ions), and potassium (as potassium ions). Inorganic commercial fertilizers are easily transported, stored, and applied. Worldwide, their use increased about tenfold between 1950 and 1989 but declined by 12% between 1990 and 1999. Today, the additional food they help produce feeds one of every three people in the world, without them, world food output, would drop an estimated 40%.
Commercial inorganic fertilizers have some disadvantages, however. These include (1) not adding humus to the soil, (2) reducing the soil’s content of organic matter and thus its ability to hold water (unless animal manure and green manure are also added to the soil), (3) lowering the oxygen content of soil and keeping fertilizer from being taken up as efficiently, (4) typically supplying only two or three of the twenty or so nutrients needed by plants, and (5) releasing nitrous oxide, a greenhouse gas that can enhance global warming. The widespread use of commercial inorganic fertilizers, especially on sloped land near streams and lakes, also causes water pollution as nitrate and phosphate fertilizer nutrients are washed into nearby bodies of water. The resulting plant nutrient enrichment causes algae blooms that use up oxygen dissolved in the water, thereby killing fish.
How is paragraph 7 related to paragraph 6?
¡ Paragraph 7 presents the drawbacks of a practice that paragraph 6 presents as an advantage.
¡ Paragraph 7 argues that the viewpoint presented in paragraph 6 is based on several factual errors.
¡ Paragraph 7 provides supporting evidence for some of the claims made in paragraph 6.
¡ Paragraph 7 contrasts recently developed practices with the more traditional, established ones discussed in paragraph 6.
Commercial inorganic fertilizers have some disadvantages, however.
此句话中一个表示转折关系的词 however. 说明第七段和第六段是转折关系。第七段主要内容为商用无机肥料有一些缺点，那么第六段反过来说的就是商用无机肥料的优点。因此这题选A。
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.
The widespread use of commercial inorganic fertilizers, especially on sloped land near streams and lakes, also causes water pollution as nitrate and phosphate fertilizer nutrients are washed into nearby bodies of water.
¡ The main cause of water pollution is the widespread use of commercial inorganic fertilizers on sloped land near streams and lakes.
¡ In addition, the widespread use of commercial inorganic fertilizers causes water pollution when nitrates and phosphates are washed into streams and lakes.
¡ Also, the widespread commercial production of inorganic fertilizers has caused water pollution in bodies of water such as streams and lakes.
¡ The most commonly used commercial inorganic fertilizers are nitrate and phosphate fertilizers, which cause water pollution if they enter streams or lakes.
接下来我们先可以通过逻辑对应优先找到B和C选项可能是答案。C选项错误在把streams and lakes 作为一个例子成分，然而原句中小溪和河流应该是一个时间状语成分，因此此题选B.