GWD一题的答案求证

evelyn205205

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
   
   这道题来自GWD,ANSWER给的是A,答案错了是吧，应该选的是C吧。
   
   
   

夜幕如斯

prep的答案是C

evelyn205205

好，谢谢！

Oliviajobs

嗯， 我也倾向C

evelyn205205

恩，A的答案明显是错的，哎，这GWD答案太坏。。。