To be sure that one insect pest will not be traded for another when an insecticide is used, scientists must perform careful experiments and do wide research. The experiments and research provide knowledge of the possible hazards an insecticide may bring to plant and animal communities. Without such knowledge, we have found that nature sometimes responds to insecticides in unexpected ways.

　　21. An insecticide was used in Louisiana to kill the troublesome______.

　　A. corn borer B. Japanese beetle

　　B. gypsy moth D. fire ant

　　22. While it is not directly stated, the article suggests that______.

　　A. insecticides are not dangerous to any small animals

　　B. insecticides do not always accomplish their purposes

　　C. insecticides are no longer being used to kill insects

　　D. insecticides do no harm to people

　　23. On the whole, the article tells about______.

　　A. the appetites of plant-eating insects B. the best way to kill boll weevils C. the dangers in using insecticides D. the best way to grow crops

　　24. Which statement does this article lead you to believe?

　　A. All changes are predictable. B. Nothing ever changes in nature.

　　C. Nature is not always predictable. D. Nature always serves man well.

　　25. Scientists perform careful experiments and do wide research because______.

　　A. they must learn to destroy all the insects that we need

　　B. they must be sure one insect pest is not traded for another

　　C. research keeps them from inventing new insecticide for the crops

　　D. research helps them find a way to kill all insects

　　21. D 22. B 23. C 24. C 25. B

　　Every day 25 million U. S. children ride school buses. The safety record for these buses is much better than for passenger cars; but nevertheless, about 10 children are killed each year riding on large school buses, and nearly four times that number are killed outside buses in the loading zones. By and large, however, the nation's school children are transported to and from school safely.

　　Even though the number of school bus casualties(死亡人數(shù)) is not large, the safety of children is always of intense public concern. While everyone wants to see children transported safely, people are divided about what needs to be done—particularly whether seat belts should be mandatory (強(qiáng)制性的)•

　　Supporters of seat belts on school buses argue that seat belts are necessary not only to reduce death and injury, but also to teach children lessons about the importance of using them routinely in any moving vehicle. A side benefit, they point out, is that seat belts help keep children in their seats, away from the bus driver.

　　Opponents of seat belt installation suggest that children are already well protected by the school buses that follow the National Highway Traffic Safety Administration's (NHTSA) safety requirement set in 1977. They also believe that many children won't wear seat belts anyway, and that they may damage the belts or use them as weapons to hurt other children.

　　A new Research Council report on school bus safety suggests that there are alternate safety devices and procedures that may be more effective and less expensive. For example, the study committee suggested that raising seat backs four inches may have the same safety effectiveness as seat belts.

　　The report sponsored by the Department of Transportation at the request of Congress, reviews seat belts extensively while taking a broader look at safety in and around school buses.

　　26. Each year, children killed outside buses in the loading zones are about_______.

　　A. 10 B. 40

　　C. 30 D. 50

　　27. Which of these words is nearest in meaning to the words "are divided" in Paragraph2?

　　A. disagree B. separate

　　C. arrange D. concern

　　28. According to the passage, who has the greatest degree of control of the school buses' "safety"?

　　A. A New Research Council.

　　B. The Department of Transportation.

　　C. The Medical Organizations.

　　D. National Highway Traffic Safety Administration.

　　29. It may be inferred from this passage that_______.

　　A. many of the opponents of seat belt installation are parents and officials of the Department of Transportation

　　B. proposal of seat belts on school buses would be seriously considered

　　C. an alternate safety device (raising seat backs four inches) may be taken into　consideration

　　D. The Department of Transportation may either take the idea of seat belts or other measures when it reviews the whole situation

　　30. The best title which expresses the idea of the passage is_______.

　　A. Making School Buses Even Safer for Children

　　B. Seat Belts Needed on School Buses

　　C. Alternate Safety Devices and Procedures

　　D. Safety in and around School Buses

　　26. B 27. A 28. D 29. D 30. A