牛牛帮忙！------ Verbal 17 CR-146

adsdsd

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 __________.
A. neither the predators nor the parasites of leaf beetles themselves attack willow trees
B. the parasites that attack leaf beetles actually tend to be more prevalent in areas with severe air pollution than they are elsewhere
C. the damage caused by leaf beetles is usually not enough to kill a willow tree outright
D. where air pollution is not especially severe, predators have much more impact on leaf-beetle populations than parasites do
E. willows often grow in areas where air pollution is especially severe



Answer： D




看完OG解释还是不明白D为什么是对的，请NN帮忙解释一下！

OG解释如下：
Situation
Leaf beetles damage willow trees, but predators and parasites keep leaf beetle populations in check. Air pollution reduces populations of predators but not of parasites. Leaf beetles damage willows especially severely in areas with severe air pollution.
Reasoning
What would support the conclusion that air pollution’s effects on the predator populations (but not on the parasite populations) explains why leaf beetles damage willows the most in areas with severe air pollution? The word since preceding the blank space at the end of the passage indicates that the space should be filled with a premise supporting the conclusion stated immediately before the since. To support this conclusion, it would help to have evidence that predators play a predominant role in keeping leaf beetle populations in check, and thus that the reduction of predator populations by air pollution could be sufficient to enable leaf beetle populations to grow and cause especially severe damage.
A   The fact that neither the predators nor the parasites directly contribute to harming the trees offers no reason to conclude that a difference in how they are affected by pollution would contribute to the harm that the beetles cause to the trees.
B   If the parasites are more prevalent in areas with severe air pollution, then they are more likely to keep leaf beetle populations in check in those areas, despite the reduced predator populations. Thus, the decline in predator populations would more likely be insufficient to explain why the leaf beetles cause more damage in those areas.
C   This observation is irrelevant to whether the decline in predator populations explains why leaf beetles damage willow trees more severely in areas with severe air pollution.
D   Correct. This indicates that predators play a predominant role in keeping leaf beetle populations in check, so, as explained above, it supports the argument’s conclusion.
E   This is not clearly relevant to whether the decline in predator populations explains why leaf beetles damage willow trees more severely in areas with severe air pollution. The argument’s conclusion could just as easily be true regardless of whether willows grow in such polluted areas frequently or infrequently.

Bradz

天敌和寄生虫都有控制昆虫的作用。已知在污染地区，天敌变少，寄生虫数量不变，昆虫的破坏还是很大。说明天敌对昆虫的控制远远大于寄生虫对昆虫的控制，既D选项所说的。

adsdsd

Bradz 发表于 2016-10-17 14:09
天敌和寄生虫都有控制昆虫的作用。已知在污染地区，天敌变少，寄生虫数量不变，昆虫的破坏还是很大。说明天 ...

明白了，大概是这个意思：
问以上发现可以解释why leaf beetles cause particularly severe damage to willows in areas with severe air pollution的原因
air pollution严重——predator数量下降——Leaf beetles数量上升——willow受损严重（因为predator对willow的影响比parasite对willow的影响大才有这个明显的比较）

还想问一个问题：D选项强调 where air pollution is not especially severe是为什么呢？
似乎说where air pollution is especially severe就不是这样？我一开始因为这个原因才排除D项的

Bradz

我觉得你过度解读了这个'not'。

这道题问的是：为什么在污染环境中，parasites不能很好地控制leaf beetles。题干中researchers已知（1）parasites和predators的组合可以控制leaf beetles，（2）但是predators不能在污染环境中存活，所以我们能够得知researchers一定是在非污染环境中得出的以上结论。

所以这个'not'不是想说，污染和非污染环境中，parasites和predators的工作机制会不一样；而仅仅是表明了得出（1）的实验基础。

adsdsd

Bradz 发表于 2016-10-18 08:39
我觉得你过度解读了这个'not'。

这道题问的是：为什么在污染环境中，parasites不能很好地控制leaf beetles ...

解释得太棒了

kennichan2011

感谢分享！               

likejiayuan

ls说得真的对吗？

填空应该是另起一个原因，跟parasite不一样，标志是nevertheless和分号。

D是另起一个原因，就是强调pradator的作用。