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 nonindigenous plants currently account for nearly 20 percent of North America’s plant species. Yet 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 nonindigenous species.
1. The passage is concerned primarily with
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.
答案是A作者: 蜜柑123 时间: 2017-8-31 20:41:00
我觉得B 中 for conflicting data 不对 例子是解释前面however的那个观点的 而不是B中的对这个数据的解释