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    本题由lindy提供
3513次学习

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 or 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.

The passage suggests which of the following about the blue

butterfly mentioned in the highlighted text?


    (A) The blue butterfly's survival was indirectly dependent on sustaining a rabbit population of a particular size.

    (B) The blue butterfly's survival was indirectly dependent on sustaining large amounts of vegetation in its habitat

    (C) The blue butterfly's survival was threatened when the ants began preying on its offspring.

    (D) The blue butterfly was infected by the virus that had been intended to control rabbit populations.

    (E) The blue butterfly was adversely affected by a biocontrol agent that competed with it for resources. 


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答案:
A
(A)Correct. 蓝
色蝴蝶的生存依赖于兔子的数量维持在一定的水平。原文说蓝蝶依靠蚂蚁的巢穴生存(保护后代):一定数量的兔子=一定数量的蚂蚁巢穴(不会“reducing蚂蚁的巢穴”),所以这个选项是正确的。 (B)蓝色蝴蝶的生存依赖于在其栖息地维持大量的植被。文中明确说明了蓝蝶的考兔子造的巢穴生存的。如果没有了兔子,植被再多也没法造巢穴。 (C)蓝蝶的生存在蚂蚁开始捕食蓝蝶的后代时受到了威胁。文中没有提到蚂蚁和蓝蝶的关系。 (D)蓝蝶感染了用来控制兔子数量的病毒。文中没有提到蓝蝶感染病毒。 (E)蓝蝶被生物控制说反作用的原因是这些生物占有了蓝蝶的资源。文中定位部分说的很清楚,蓝蝶是因为没有了兔子,才没有了哺育后代的地方。和生物是否与它们抢夺资源无关。

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