He had collected plenty of historical evidence, proved that humans used to have different

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A. that
(答案→)B. which
C. it
D. what
解析：考察定语从句。本题定语从句的先行词是plenty of historical evidence,后面的定语从句中的关系代词which指代先行词在句中作主语，that不能引导非限制性定语从句，it和what不能引导定语从句。句意：他已经收集了很多的历史证据，这些证据证明人类过去常常有不同的睡眠的方式。故B正确。