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 我选的A,在GMAT CLUB 上看人讨论有不少选了C,新东方给的答案居然是E?! 呵呵,希望大家帮忙分析一下,汗.......... |