PREP 2 - Essay 2 #7

filman

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.

Question #7.  091-06      (21560-!-item-!-188;#058&000091-06)

 

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.

答案是A

不明白为什么E不对？搜了一下没有找到满意的解释，所以提出来请NN帮忙解答！谢谢

alanfu

以下是引用filman在2008-6-23 22:15:00的发言：

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.

Question #7.  091-06      (21560-!-item-!-188;#058&000091-06)

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.

答案是A

不明白为什么E不对？搜了一下没有找到满意的解释，所以提出来请NN帮忙解答！谢谢

 我也觉的答案是E吧，however之后，biocontrol agents can negatively affect nontarget species by, for example, competing with them for resources；another

example。。。。。

auroral1982

再顶顶，希望大家帮忙看看！！！谢谢了！

auroral1982

是不是这样呢？

However, biocontrol agents can negatively affect nontarget species （1） 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. （2）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.

however后面一共举了两个例子来说明生防作用物的负面影响。E选项给出的是第一个例子的内容。而butterfly是第二个例子里面提到的，自然不能用第一个例子的里面的概括。而A选项虽不明显，细看却是简简单单的给出了第二个例子的概括，butterfly在一定地区内（in England）和兔子数量是有关系的。

cleoguo

同问~

hughlv

感觉auroral1982的回答比较在理。bufferfly和rabbit并不是直接的竞争关系，只是rabbit间接导致了bufferfly的生存问题。

cloudballoon

舉了兩個例子
E把這個描述成了第一個例子
A很明確是第二個例子的定位

所以 A