More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect nontarget species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs.

Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in 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 of disruptions 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 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, determining the potential 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, so that it can feed on or otherwise harm new hosts.

24-5 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

我选B, 答案是D

请教大家

这题我也在奇怪中。

B是不对的。因为文中只提到了extinction，未提到proliferation

D答案是因为语法问题：

(D) Diminution of the positive effects conferred by a nontarget animal species

我初看上去，立即判错。但后来没找到答案。。

后来发现，原来D答案还有一种理解方式。

(D) Diminution of the positive effects conferred by a nontarget animal species

这个这个~~~

你怎么看？

line 2: However, biocontrol agents can negatively affect nontarget species ...

extinction只是一种情况啊

主要是针对nontarget species ...