gwd-11-41

Q41:

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old.  Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.

Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?

1. Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.


2. Another campsite was found in New Mexico with remains dated at 16,000 years old.


3. A computer simulation of glacial activity showed that it would already have been impossible for humans to travel south overland from Alaska 18,500 years ago.


4. Using new radiocarbon dating techniques, it was proved that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge at least 11,400 years ago.


5. Studies of various other hunting-gathering populations showed convincingly that, once the glaciers allowed passage, humans could have migrated from Alaska to Colorado in about 20 years.

   Answer: cD

请问这到题目的思路是什么，毫无头绪！！！

啊，突然想起来了。看样这样的题目要，充分理解题目才行

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old.

推出木炭=11，200years

Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.

有因为上面这个时间限制，所以人类活动留下的记录要么大于18，000，要么小于11，000，有因为木炭=11，200years，所以，排除小于11，000的可能性，research选择了大于18，000。

d答案提出了人类有可能在11，200年前来到american，也就是说为木炭=11，200years，提供了解释，因此weaken了题目。