大家能否指点一下天山7－Q41啊

天山7－Q41:>>

Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a>>

dry riverbed in the Afar region of LACE>EthiopiaLACE> 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

答案是C，但是我觉得A合适。date 后面跟when没有问题。但C用完成时第一个就被我否决了。向各位请教。

没错，应该选C.

A的错误在于：

1.介词+which优先于when,where

2.it无所指

3.动词不定式的完成时态表示不定式动作发生在位于动词之前，在know之前就已经made

sorry Iam not convinced.

1) prep + which 优于when 是相对错误

2) it 指代that主语从句

3）人类制造石器的时间已经给出，发生在某个具体的时间点的事情用过去时

C改变句子重心和意思，不是很好。

have made看了也不爽。

坚决选A

我觉得前人讨论的蛮完整的