2. 外语
  3. There have been numerous well-documented extinctions of indigenous species caused by the introduction of non-indigenous predator

There have been numerous well-documented extinctions of indigenous species caused by the introduction of non-indigenous predator

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问题     There have been numerous well-documented extinctions of indigenous species caused by the introduction of non-indigenous predators and pathogens. However, surprisingly few extinctions of indigenous species can be attributed to competition from introduced species. For example, during the past 400 years, 4,000 plant species have been introduced into North America, and these non-indigenous plants currently account for nearly 20 percent of North America’s plant species. Yet that no evidence exists that any indigenous North American plant species became extinct as a result of competition from new species could mean that such extinctions take longer to occur than scientists initially believed or, alternatively, that extinctions are rarely caused by competition from non-indigenous species.
The author introduces statistics about North America’s non-indigenous plant species primarily in order to
选项 A、undermine a proposed explanation for the absence of any evidence for the occurrence of a particular phenomenon
B、contrast the effect of introduced plant species in North America with the effect that introduced animal species have had
C、suggest that North America’s indigenous plants are a domain in which there has been ample scope for a particular effect to have occurred
D、emphasize how much the ecology of North America has been affected over the past 400 years by the introduction of non-indigenous species
E、substantiate a claim about the overall effect that the introduction of non-indigenous species tends to have on indigenous populations
答案E
解析 本题属于功能题。定位到第三句。定位句是数据，因此是一个证据，而证据的功能就是用来支持观点的，因此E的表述正确。the overall effect指的是引入外来物种后，并没有通过竞争来导致当地物种灭亡。因此这个数据可以证实作者在第二句的观点——很少有竞争导致的灭绝。A项文章给出解释是在最后一句，定住句的数据只能用来支持前面的观点，无法削弱后面的解释。B项文章没提动物物种。C项作者引用外来物种的数据，其侧重点在外来物种所产生的影响，和当地物种是否是一个充分的领域无关。另外，该选项可以看作是作者引用北美种群数据的原因，而非目的。D项定位句只涉及北美的植物种群，ecology的范围太大。
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