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题库 / OG2017V-CR-146
Which of the following most logically completes the passage?
Leaf beetles damage willow trees by stripping away their leaves, but a combination of parasites and predators generally keeps populations of these beetles in check. Researchers have found that severe air pollution results in reduced predator populations. The parasites, by contrast, are not adversely affected by pollution; nevertheless, the researchers' discovery probably does explain why leaf beetles cause particularly severe damage to willows in areas with severe air pollution, since __________.
neither the predators nor the parasites of leaf beetles themselves attack willow trees
the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere
the damage caused by leaf beetles is usually not enough to kill a willow tree outright
where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do
willows often grow in areas where air pollution is especially severe
果因推理
果-树惨遭损害
因-污染 加强污染这个原因
A 污染无关
B 寄生虫和捕食者都有控制作用，这里讲寄生虫多，不知道是污染的原因还是寄生虫控制原因
C 污染无关
D 没有污染时，捕食者的作用比寄生者大的多，意思就是寄生者只是辅助，重点控制beetle还是要捕食者控制。那污染来了，捕食者没了，寄生者自然没什么用。解释确实是污染导致的
E 树喜欢长在污染区。 没法解释为什么伤害的多
B仔细想想可以直接排除。如果parasite多，那么beetles不是应该减少吗？怎么会对树造成更严重的影响呢？我脑筋也是瓦特了。
捕食者数量下降，杀虫剂没受影响，但是beetle的数量上升了。说明真正对beetle起抑制作用的肯定是捕食者
D. this indicates that predators play a predominant role in keeping leaf beetle populations in check.
a combination of parasites and predators generally keeps populations of these beetles in check.
说明在污染严重的地方parasites and predators不平衡，那么答案要讲出两者不平衡的状态，光体现parasites不够
BD 纠结；最后还是选错了
严重超时+做错