天山7-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
答案是C,但是我觉得A合适。看过以前的讨论帖,不多,就一贴,说服不了我。C用完成时第一个就被我否决了。向各位请教。 |