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  3. The sustained massive use of pesticides in farming has two effects that are especially pernicious. First, it often kills off the

The sustained massive use of pesticides in farming has two effects that are especially pernicious. First, it often kills off the

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问题 The sustained massive use of pesticides in farming has two effects that are especially pernicious. First, it often kills off the pests’ natural enemies in the area. Second, it often unintentionally gives rise to insecticide-resistant pests, since those insects that survive a particular insecticide will be the ones most resistant to it, and they are the ones left to breed.
From the passage above, it can be properly inferred that the effectiveness of the sustained massive use of pesticides can be extended by doing which of the following, assuming that each is a realistic possibility?
选项 A、Using only chemically stable insecticides
B、Periodically switching the type of insecticide used
C、Gradually increasing the quantities of pesticides used
D、Leaving a few fields fallow every year
E、Breeding higher-yielding varieties of crop plants
答案B
解析 Evaluation of a Plan
Situation Continued high-level pesticide use often kills off the targeted pests’ natural enemies. In addition, the pests that survive the application of the pesticide may become resistant to it, and these pesticide-resistant pests will continue breeding.
Reasoning What can be done to prolong the effectiveness of pesticide use? It can be inferred that the ongoing use of a particular pesticide will not continue to be effective against the future generations of pests with an inherent resistance to that pesticide. What would be effective against these future generations? If farmers periodically change the particular pesticide they use, then pests resistant to one kind of pesticide might be killed by another. This would continue, with pests being killed of in cycles as the pesticides are changed. It is also possible that this rotation might allow some of the pests’ natural enemies to survive, at least until the next cycle.
A Not enough information about chemically stable insecticides is given to make a sound inference.
B Correct. This statement properly identifies an action that could extend the effectiveness of pesticide use.
C Gradually increasing the amount of the pesticides being used will not help the situation since the pests are already resistant to it.
D Continued use of pesticides is assumed as part of the argument. Since pesticides would be unnecessary ror fallow fields, this suggestion is irrelevant.
E Breeding higher-yielding varieties of crops does nothing to extend the effectiveness of the use of pesticides.
The correct answer is B.
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