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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 it is known that humans had made
D that humans are known to be making A
E of humans who were known to make 天山答案C，XDF答案E 。我觉得BC时态错，D to be doing 这个结构错，但具体为什么错不懂，只是觉得一般出现它肯定不选~~~ | 
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发表于 2009-4-1 22:35:00
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