一道大全应该有的题，但是我不知道题号。求助各位，谢谢大家

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 150,000years the earliest date when it is known that humans made stone tools.

A.同上

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e.date表时间不是应该用when的吗？请教各位。

date后面的内容都是修饰date的 表示石器时代时期

如果用 date when 表达石器时代出来的句子是：date when human are known to... when像是引导了时间状语

谢谢你的回答

可是时间状语从句为什么不对呢？

首先，date at是估计句式；

其次，介词+which优于when

最后，when经常有歧义，可以指代时间，可以做“当。。。”这个是什么从句忘了。

一般，when只跟在时间后面，比如.....in 2007，when....

所以这题when没一点是对的，在gmat语法中

pushing back by more than 150,000years the earliest date 如果没理解错的话 应该是个倒装结构，正序是

pushing the earliest date (when it is known that humans made / of humans who were known to make) back by more than 15000 years

根据题目要表达的意思，黄色部分为date的定语，when怎么能引导定语呢