T-4-Q1 天山-7-41 again
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.
when it is known that humans made
at which it is known that humans had made
at which humans are known to have made
that humans are known to be making
of humans who were known to make
查了之前的帖子，还是疑惑！
1.date 用when 或者 at which修饰都可
2. 关于时态，还是得建立在理解整句话的意思上，科学家确认尖石的年代是。。。，把人类最早使用石具的记录向前推了150000多年。（pushing back句是个小倒装，应为:pushing back the earlist date at which ...by more than 150000 years）
因此at which humans are known用现在时是对的，表示目前所有的记载，制造石器比are known要早，所以现在完成时和过去时都可以咯
那为什么A 不对？？？
-- by 会员 audreyzhang2 (2010/2/26 10:19:45)
