請教GWD21-34

GWD 21-34

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

我選c  可是這題答案是a   可以幫我看看嗎? 謝謝

21？

楼主能不能分享此套题啊

此题中at which和when可通用，C的问题是时态不对，语义也改变乐，有：那个时候（就被人知道）...，而不是现在（被人知道那个时候）...

in which和where, at which和when在某些情况下是可以通用的，语法书中是如此说，但GMAT中似乎更倾向于使用where和when~~，如果没有其它错误，可以考虑此点，但此点不是绝对错误，只是相对错误~~

答案是A吗?

为什么我下载的这份答案是C?

Can you tell me where I can download answer?

这道题的答案我下载的也是c

怎么会事？

开始我也选择C ,再看一便的时候发现时态不对头,改成was应该可以.A没有问题

A is the best

I don't agree with "A", instead, I agree with "C".

because, 請把 A 與C的從句分別還原回去, 會變成:

A)  [That humans made stone tools] is known [the earliest date]

when 變成修飾 is ,  邏輯不合.

D) humans are known to have made [the earliest date]

at which 修飾have made, 邏輯合.

有沒有人同意這樣的view?