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Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools. A. when it is known that humans made B. at which it is known that humans had made C. at which humans are known to have made D. that humans are known to be making E. of humans who were known to make
A. 关系代词用when和at which都是可以的,这里更偏向后者，因为when是要跟具体的时间；A的意思是把知道这个事实的日期往前推了，而C的意思是这个事实被往前推了，但know还是发生在现在的；
关于这道题的用at which 还是when 的逻辑问题不太明白，解释中说的“A的意思是把知道这个事实的日期往前推了，而C的意思是这个事实被往前推了”是什么意思？搜了一些帖子没有很理解，麻烦NN解答
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发表于 2014-10-19 10:01:46
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