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.

(Line 14)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 (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, 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

The answer is D. But did anyone notice that in question"conferred by a NONTARGET animal species" whereas in article "conferred by a target animal species"?

I changed my idea from D to B.

但是B proliferation of a nontarget animal species没有发生吧... nontarget animal 数量减少了..

选D的直接证据：

原文第一段末尾

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.

和D做个对比：

Diminution of the positive effects conferred by a nontarget animal species

D的间接证据：

看第二段开头的another example of indirect negative consequences。看到another一定要注意，要想这说明作者把上一件事情也定义为indirect negative consequences，那上一件事情就非常可能是考点。

B说proliferation错，这里没有增长得。

ps：大家不要怕占地方，把原文按正式得格式贴出来，字大点大家看着方便。