标题: 求解一道 GWD ，答案到时是C还是D [打印本页] 作者: zdf6441634 时间: 2011-1-10 10:43 标题: 求解一道 GWD ，答案到时是C还是D Scientists have dated sharp-edged flakes of stone found inthe fine-grained sediments of a dry riverbed in the Afar region of Ethiopia tobetween 2.52 and 2.60 million years ago, pushing back by more than 150,000years 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 作者: sdcar2010 时间: 2011-1-10 11:13
at which humans are known to have made
is the answer.作者: zdf6441634 时间: 2011-1-10 11:32
Thank you.