P1 There are recent reports of apparently drastic declines (Anecdotal reports of population decreases ) in amphibian populations and of extinctions of a number of the world's endangered amphibian species.
An endangered population is always rare(A), almost always small(B), and, by definition, under constant threat of extinction(C) even without a proximate cause in human activities(E).---->D
我的思路：
选项A正确，未划线部分出现了现在完成时，意味着划线部分中必须有一个过去的时间点，此选项中35 years after the release of African honeybees 即为这个时间点。因此逻辑上时间线为： release honeybees—> migrate —> 35 years after the release。
选项B since是现在完成时的标志，不可以和had migrated同时出现；their descendants成了releasing的主语，不符合逻辑语义；In less than 35 years……做时间状语修饰had migrated显然不符合逻辑。
选项C since是现在完成时的标志，不可以和had migrated同时出现In less than 35 years……做时间状语修饰had migrated不符合逻辑
选项D it 作形式主语的正确句式是：It took some time to do something
选项E 同上
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错选C：蚊帐可以为除了蚊子之外的其他昆虫提供保护，违背了premise