The world population is growing at a rate of about 90 million people per year, with the Third World accounting for 80 million of them. The pressure on cities can only go on increasing. The urban population of the developing countries will exceed 2 billion people by the year 2000 and since the main reason for the high demographic (人口統計的) growth is poverty, the additional population will be mostly made of people of very limited means.

　　21. If the urban population of the developing countries exceeds 2 billion people by the year 2000, the main problem the additional people will face is______.

　　A. housing B. food

　　C. poverty D. limited land

　　22. According to the passage, "about US $116 billion is required to give minimum comfort to these people by the turn of the century—less than US $ 10 billion per year. " Do you think which year was the article written by saying "less than $ 10 billion per year" by the turn of the century?

　　A. 1985. B. 1990.

　　C. 1988. D. 2000.

　　23. The mankind should face the phenomenon that the world has become a world of cities with______.

　　A. a lot of difficulties

　　B. efforts to improve housing condition

　　C. pressure of the basic needs

　　D. new models and a great deal of transformation of ideas and methods

　　24. In Africa, people in cities will be______by the end of the century.

　　A. almost twice as much as in 1985 B. doubled than that in 1985

　　C. over twice as much as in 1985 D. 300 million

　　25. In spite of the efforts to improve housing condition, the number of people living in shanty-towns will increase because______.

　　A. houses in shanty-towns are cheap

　　B. shanty-towns could provide people with minimum comfort

　　C. no policy will be capable of stopping or changing the present immigrant tendency from the rural areas to the cities in the Third World

　　D. the Third Word population is growing at a rate of about 80 million people per year

　　21. C 22. C 23. D 24. C 25. C

　　Agriculture is the number one industry in the United States and agricultural products are the country's 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 nation's 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 nation's 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 nation's water supply

　　26. D 27. B 28. B 29. C 30. A