|
1.有一篇GWD的阅读,就是生物天敌的那一片文章
估计是这个
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.
24-3 The passage is primarily concerned with
(A) explaining why until recently scientists failed to recognize the risks presented by biocontrol agents.
(B) emphasizing that biocontrol agents and chemical pesticides have more similarities than differences.
(C) suggesting that only certain biocontrol agents should be used to control plant or animal pasts.
(D) arguing that biocontrol agents involve risks, some of which may not be readily discerned.
(E) suggesting that mishaps involving biocontrol agents are relatively commonplace.
24-4 The passage suggests that the author would be most likely to agree with which of the following statements about the use of biocontrol agents?
(A) Biocontrol agent should be used only in cases where chemical pesticides have proven ineffective or overly dangerous.
(B) Extinctions and disruptions resulting from the use of biocontrol agents are likely to have increasingly severe commercial consequences.
(C) The use of biocontrol agents does not require regulation as stringent as that required by the use of chemical pesticides.
(D) The use of biocontrol agents may even finally supersede the use of chemical pesticides in controlling unwanted species.
(E) The risks of using native biocontrol agents may be easier to predict than the risks of using nonnative biocontrol agents.
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
24-6 The example presented by the author in lines 14-23 most clearly serves to illustrate
(A) a situation in which a species is less vulnerable to biocontrol agents than it would have been to chemical pesticides.
(B) a way in which the introduction of a biocontrol agent can affect a nontarget species.
(C) a nonnative agent’s adapting in an unpredictable way that results in damage to a new host.
(D) the contention that biocontrol agents can harm nontarget species by competing with them for resources.
(E) the way in which indirect consequences from the use of biocontrol agents are most likely to occurs. | 
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2005-11-18 22:28:00
楼主
