各路英雄请会战 GMAT 真题21 - 34

bluestone1

34. Scientists have dated sharp-edges 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

Snazzy

i prefer to B

roblixtt

D?

Allen

Ｅ

ios

d

date's "tong wei yu"

ecsniffer

A

ios

oh，应该是A

lizaz

A

solome

A

yongchou

date at which
date when
date  that----- all OK,
The key is "known to have made", as in "Neandertals are known to have made stone tools
and weapons."-------that's C , I guess