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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.
果因
∴partridge（P）数量减少
∵没有P接触除草剂的证据，所以是其他原因导致P减少
削弱，即说明P减少就是因为除草剂，排除他因or增强链条
A、种子因为杀虫剂减少→P吃的昆虫减少（从直接毒P到间接毒P，还是除草剂的锅，跟其他原因无关），CQ2，CORRECT
B、P很珍贵，记录它数量要比记录别的鸟更仔细；无关，甚至他因增强
C、除草剂不影响谷物产量；无关
D、其他住在附近的鸟也在减少；无关
E、如果动物消化了除草剂中的毒素，毒素是可以被识别的；他因增强
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