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题库 / Prep2007E2-CR-22
Herbicides allow cereal crops to be grown very efficiently, with virtually no competition from weeds. In Britain, partridge populations have been steadily decreasing since herbicide use became widespread. Some environmentalists claim that these birds, which live in and around cereal crop fields, are being poisoned by the herbicides. However, tests show no more than trace quantities of herbicides in partridges on herbicide-treated land. Therefore, something other than herbicide use must be responsible for the population decrease.
Which of the following, if true about Britain, most seriously weakens the argument?
The elimination of certain weeds from cereal crop fields has reduced the population of the small insects that live on those weeds and that form a major part of partridge chicks' diet.
Since partridges are valued as game birds, records of their population are more carefully kept than those for many other birds.
Some of the weeds that are eliminated from cereal crop fields by herbicides are much smaller than the crop plants themselves and would have no negative effect on crop yield if they were allowed to grow.
Birds other than partridges that live in or around cereal crop fields have also been suffering population declines.
The toxins contained in herbicides typically used on cereal crops can be readily identified in the tissues of animals that have ingested them.
Argument: 由于在鸟的体内检测不到大量的农药，所以农药中毒不是导致鸟的数量减少的原因。鸟的数量减少是由于农药之外的其他因素。
反驳Argument：即使鸟类不是因为”农药中毒“而导致数量减少，”农药本身“仍然是导致鸟数量减少的因素。换句话说，我们要找的选项是能够证明农药通过其他途径导致鸟的数量减少（不是用鸟类中毒这种方式）。
现在看选项A: 使用农药导致野草数量下降，野草数量下降导致虫子减少，虫子减少导致鸟类食物减少，食物减少导致鸟的数量下降。所以农药通过间接使鸟类食物减少的方式导致了鸟数量的decline。选A。
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