大牛請给我讲讲这道题啊，谢谢了

bernadotte

Q41:

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

zylrt

这是一道GWD的争议题
我选择的是A，刚刚google了一些帖子，包括老外的论坛
正确答案是什么？有说A的，也有说C的
D/E上来就是可以排除的
个人觉得A好是因为时态的原因，在定语从句修饰的这个date，特定的时期内发生的事情，所以用made
但是B/C的选项，有争议，是因为at which和when的区别。有帖子说，at which优于when，这个我也在疑惑。所以不甚明白

请NN详解

果汁软糖

觉得选C  划线部分应该是做date的修饰语，而A和B里面的it无所指，E里面的表达逻辑错误，D的时态不对，C里面的have made应该是到date的时间点为止已经make了的意思吧…… at which的表达比when更准确一点
个人观点，仅供参考

francoiswang

同意楼上，at which跟能表示是在一个精确的时间点，如at 1999；it可以指代不定式和that后面的这件事，但个人觉得be known to do比较常用，个人观点而已，有错请指出

bernadotte

的确是GWD里面的題，给的答案是A。我下载的是31套題版本。

我选择了C，尽管对at xxx date不是很满意，通常都是on xxx date。不过it is...好象也太罗嗦了些，而且那个it指代什么呢，that从句吗？读起来其实貌似也不怎么合乎句子的意思的，有歧义。

再次读读倒是感觉A稍好些了。关键是怎么理解。。。。。。

期盼更令人信服的解释，版主谈谈吧