T-4-Q1 TS-7-41Scientists 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 答案就是C,用的就是humans are known 不是说问题的关键在一个是人,一个是动物吧?
或者说sb be known/said之类的只可以加to do 吧?
请指教!
|