Passage 4Agriculture is the number one industry in the United States and agricultural products are
Agriculture is the number one industry in the United States and agricultural products are the countrys leading export. American farmers manage to feed not only the total population of the United States, but also millions of other people throughout the rest of the world. Corn and soybean exports alone account for approximately 75 percent of the amount sold in world markets.
This productivity, however, has its price. Intensive cultivation exposes the earth to the damaging forces of nature. Every year wind and water remove tons of rich soil from the nations croplands.
Each field is covered by a limited amount of topsoil, the upper layer of earth which is richest in the nutrients and minerals necessary for growing crops. Ever since the first farmers arrived in the Midwest almost 200 years ago,cultivation and, consequently, erosion have been decreasing the supply of topsoil. In the 1830s, nearly two feet of rich, black top soil covered the Midwest. Today the average depth is only eight inches, and every decade another inch is blown or washed away. This erosion is steadily decreasing the productivity of valuable cropland. A United States Agricultural Department survey states that if erosion continues at its present rate, corn and soybean yields in the Midwest may drop as much as 30 percent over the next 50 years.
So far, farmers have been able to compensate for the loss of fertile topsoil by applying more chemical fertilizers to their fields; however, while this practice has increased crop yields, it has been devastating for ecology. Agriculture has become one of the biggest polluters of the nations precious water supply. Rivers, lakes, and underground reserves of water are being filled in and poisoned by soil and chemicals carried by drainage from eroding fields. Furthermore, fertilizers only replenish the soils they do not prevent its loss.
26. The last sentence in the first paragraph gives an example to show_______.
A. that American farmers manage to feed the total population of the U. S.
B. the leading position of the U. S. farming in the world
C. how important American people consider their farming
D. that many people in the world rely on the export of the agricultural products of the U. S. A.
27. In order to compensate for the loss of fertile topsoil, farmers have been_______.
A. planting less corn and soybean B. putting fertilizers on their fields
C. preventing soil erosion D. decreasing the supply of top soil
28. At the present rate, approximately how many years later the black top soil now covering the Midwest will completely be blown or washed away?
A. 120 years later. B. 80 years later.
C. 50 years later. D. 100 years later.
29. This practice in Paragraph 4 refers to_______.
A. that farmers have lowered the yield of corn and soybean
B. that farmers have expanded croplands
C. that farmers have applied more chemical fertilizers
D. that the top soil has been decreased greatly
30. All of the following are statements about the disadvantages of fertilizers EXCEPT that
A. they replenish the soil B. they do not prevent the loss of soil
C. they are destroying the ecology D. they pollute the nations water supply
答案: 26. D 27. B 28. B 29. C 30. A
混合条件句的概念
非真实条件句的应用
与后接名词或代词保持一致的情况
特殊的虚拟语气词:should
不用被动语态的情况
表示“据说”“相信”的词组
部分倒装句的应用
限制性和非限制性定语从句
only在句首要倒装的情况
It is (high) time that的用法
need "不必做"和"本不该做"
if only和only if 的区别
谓语需用单数的情况
关系副词引导的定语从句
主谓一致中的靠近原则
if, whether引导的名词从句
名词性that-从句
谓语动词与前面的主语一致的情况
定语从句的概念
感叹句的结构
wish的用法
否定转移的应用
祈使句的结构
反意疑问句的结构
主谓一致的概念
真实条件句的应用
as, though 引导的倒装句
强调句的结构
时态与时间状语
虚拟语气的概念
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