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C。。
参考答案是A
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 时态错，没有表达原意。
B. at which it is known that humans had made 事态错
C. at which humans are known to have made
D. that humans are known to be making that前应加at( 时间状语匆遽); to be making表达意思错.(C)
E. of humans who were known to make date of humans逻辑意思错
vote for A, the tense is right
答案肯定是c
known to do sth 对应do的过去时应该是
known to have done
对应的完成时是
known to have had done
(e.g. from real newspaper)
All are known to have been beaten severely on the night of March 22 at the al-Khalifa police station.
所以这里的have made 当过去时，而非完成时讲。
完全同意楼上的，选c.
我还是比较倾向于A,
我是觉得at which有问题 如果是at which，前面是个时间点比较好吧，比如来个AD XXXXXXXX啊，BCXXXX啊
it is known that .....句型,科学事实用一般现在时
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