GWD-10-41 逻辑，帮忙指点下

eshopaholic

Charcoalfrom a hearth site in Colorado, 2,000 miles south of Alaska, is known to be11,200 years old.  Researchers reasonedthat, since glaciers prevented human migration south from the Alaska-Siberialand bridge between 18,000 and 11,000 years ago, humans must have come to theAmericas more than 18,000 years ago.

Which of thefollowing pieces of new evidence would cast doubt on the conclusion drawnabove?

A.   Using new radiocarbon dating techniques, it was determined thatthe charcoal from the Colorado site was at least 11,400 years old.
B.   Another campsite was found in New Mexico with remains dated at16,000 years old.
C.    A computer simulation of glacial activity showed that it wouldalready have been impossible for humans to travel south overland from Alaska18,500 years ago.
D.   Using new radiocarbon dating techniques, it was proved that anice-free corridor allowed passage south from the Alaska-Siberia land bridge atleast 11,400 years ago.
E.    Studies of various other hunting-gathering populations showedconvincingly that, once the glaciers allowed passage, humans could havemigrated from Alaska to Colorado in about 20 years.

Laquisha

同问。。。。求指教

sdcar2010

D is the answer since it provides an evidence which allows human to enter America at least 11,400 years ago without walking over the Alaska-Siberialand bridge. Then 200 years later the decendents of these human might left the charcoal at a hearth site in Colorado. So D weakens the claim that the human must have come to the Americas 18,000 years ago.