一道GWD~

yaoxiayi

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?

A.    Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.
B.    Another campsite was found in New Mexico with remains dated at 16,000 years old.
C.    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.
D.    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.
E.    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.

答案是D，请高手解释一下题目和答案。

HotCold

题目是说：有一个已经有11200年历史的C是来自一个离A（什么美国阿拉斯加哦）向南2000mile的地方CO；但是研究者说道，因为在18，000年到11000年间，有个冰川阻止了人类从A穿越到它向南方向的大陆桥，所以人类肯定在早于18000年之前就已经到美国了；
答案D是说 使用一种新的什么什么追踪技术证明了有个ice-free corridor 其实是允许人类在至少11400年前穿越上文所说的大陆桥的；它直接削弱反对了原题中的原因，即根本就不存在这样的因果关系；
    我是这样理解的哈，不知道合理不、、、