标题: [求助]gwd阅读24-5，谢谢解答 [打印本页] 作者: Drakedragon 时间: 2008-3-20 15:13 标题: [求助]gwd阅读24-5，谢谢解答 More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol. Line agents (such as insects, fungi, and (5) viruses) eat, infect, or parasitize tar- geted plant or animal pests. However, biocontrol agents can negatively affect nontarget species by, for example, competing with them for resources: a (10) biocontrol agent might reduce the bene- fits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs. Another example of indirect negative. (15) consequcnces occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit popu- lations reduce the ground cover), in (20) turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disrup- (25) tions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by (30) indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, 4determining the potential (35) risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways. (40) so that it can feed on or otherwise harm new hosts. Which of the following is mentioned in the passage as an indirect effect of using a biocontrol agent? A Reduction of the commercial value of a desirable animal species B An unintended proliferation of a nontarget animal species C An unforeseen mutation in a target species D Diminution of the positive effects conferred by a nontarget animal species. E Competition for resources with a largest species. 请问正选D是从哪里来的，找了半天也没有，谢过
作者: apaso 时间: 2013-8-18 13:53
有没有人探讨下
先看选项，意思上排除了BCE
题目问as an indirect effect of using a biocontrol agent?
我第一反应是定位indirect，我第一遍理解原文是，上面肯定是（direct） 负面影响
，然后再会有一个indirect影响。所以答案在indirect出现之后。
再仔细品味 “another example of indirect negative exampl‘’ 可能意思是另外一个非直接的负面影响
如果是这样，上文与下文都是indirect，那么答案就是上下两段都能取。
然后看这个http://forum.chasedream.com/thread-83617-2-1.html
tips如果第三题（上面一题）的B选项有充分理由排除，这题其实用排除法也能做对。
However,biocontrol agents can negatively affect
nontarget species by, for example,
competing with them for resources: a
(10) biocontrol agent might reduce the bene-
fits conferred by a desirable animal
species by 。。。。。Another example of indirect negative
(15) consequcnces occurred in England