Over the past century, the composition of the human gene pool ______ appreciably.

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问题 Over the past century, the composition of the human gene pool ______ appreciably.

选项 A、did not change
B、has not changed
C、was not changed
D、had not changed

答案B

解析 时态题。在含有since,so far,as yet(to date),over(in)the past...等短语作状语的句子中,谓语动词常用现在完成时,故B正确。
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