GWD21-34

Fadaway

    

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.

    

 

    

1. when it is known that humans made
2. at which it is known that humans had made
3. at which humans are known to have made
4. that humans are known to be making
5. of humans who were known to make

答案是A ，我选了C，想问下A中it的指代，还有at which和when的区别

well4eva

a中的it是形式主语，指代that后面humans made...整句话。

at which指某个点

when指某个时间段

Fadaway

多谢，问下为何这里不能用at which?

weidehou

小白语法里说date 与 when 是固定搭配

wangming

我觉得A是对的，C,D,E都是被动语态，主动优于被动啊，B的时态不对。大家觉得 呢？

wangming

有哪位牛人帮忙解答一下吧