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B. To compare the effects of DDT with those of other cures.
C. To argue that the ecological balance can be damaged by chemicals.
D. To show that some chemicals can damage the health of humans and animals.
26.According to the author,what is one of the problems with DDT?
A. It also killed insects that helped farmers.
B. It could kill most of the harmful insects.
C. It caused a decrease in domestic animals.
D. It made some farmers suffer a disease which could not be cured.
27.If a farmer used DDT today,in a few years _______.
A. he would have no problems with harmful insects
B. insects would be an even greater problem for him
C. his situation would not be quite different
D. he would be in a very dangerous situation
Passage Three
Questions 28 to 30 are based on the following passage.
The standard of living of any country means the average person's share of the goods and services which the country produces.A country's standard of living,therefore,depends mainly on its capacity to produce wealth.
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Wealth" in this sense is not money,for we do not live on money but on things that money can buy :
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goods" such as food and clothing,and
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services" such as transport and entertainment.
A country's capacity to produce wealth depends upon many factors,most of which have an effect on one another.Wealth depends to a great extent(
在很大程度上
) upon a country's natural resources,such as coal,gold,and other minerals,water supply and so on.Next to natural resources comes the ability to put them to use.China is perhaps as well off as the U.S.A.in natural resources,but suffered for many years from various wars,and for this and other reasons was unable to develop her resources.Another important factor is the technical efficiency of a country's people.Old countries that have trained numerous skilled craftsmen and technicians are better placed to produce wealth than countries whose workers are largely unskilled.Wealth also produces wealth.As a country becomes wealthier,its people have a large amount of saving,and can put their savings into factories and machines which will help workers to produce more goods in their working day.
28.A country's wealth depends upon _______.
A. its standard of living
B. its money
C. its ability to provide goods and services
D. its ability to provide transport and entertainment
29.According to the passage,one might infer that a peaceful country _____.
A. will produce more wealth than any other country
B. will produce less wealth than any other country
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