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

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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