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标题: GMAT-6-41请教求解思路 [打印本页]

作者: sv2000 时间: 2005-11-11 16:04
标题: GMAT-6-41请教求解思路

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.

when it is known that humans made

at which it is known that humans had made

at which humans are known to have made

that humans are known to be making

of humans who were known to make

作者: yangsh 时间: 2005-11-11 17:33
c

作者: dori0214 时间: 2006-8-23 14:03

那个方框框是怎么弄出来的？ =.=

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