[求助]GWD6的一道题

肖小

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.

 

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

选A或E?我在两个不同的版本上看的答案不同.

  

carolhide

LZ可查下讨论连接，GWD的题目有时候答案不统一。