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  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 passage is concerned primarily with
选项 A、pointing out that a particular type of species extinction is rarely known to occur.
B、proposing a possible explanation for conflicting data about a particular type of species extinction.
C、resolving a debate about the frequency of a particular type of species extinction.
D、comparing two theories regarding possible causes of a particular type of species extinction.
E、refuting a proposed explanation for the increasingly rare occurrence of a particular type of species extinction.
答案B
解析 本题选项中的a particular type of species extinction指的是“竞争导致的灭绝”这种灭绝形式，而非灭绝的物种种类。本文的重点是解释前两句的矛盾是如何发生的，因此选项B正确。a possible explanation指的是第四句后半句所给出的解释，conflicting data指前两句的矛盾。A项竞争导致的灭绝很少发生，这是文中被解释的现象，属于细节。C项a debate在文中无对应。D项two theories在文中无对应。E项文中没提refuting，也没提increasingly  rare。
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