gwd答案D,我也看了大家的讨论贴。但是为何C不对？C说18500年不可以哦，难道18000-18500年之间也要考虑马？谢谢各位！！！

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.

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

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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.

你没看懂题目吧！

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

Ch=11200 （即HUMAN>11200)

Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago,

[11000, 18000]被排除

humans must have come to the Americas more than 18,000 years ago.

推出HUMAN>18000

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.

条件2被扩大为[11000，18500]被排除

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.

条件2被缩小为[11400，18000]被排除。

C已经有11200年了，说明人在11200年时就在这里，他们是刚来或是之前来的。〉11200

人是什么时候来的呢？研究者认为：冰川使人不可能11000-18000年以前来到这里，所以人是18000之前就在那了。

weaken: 它因——没有冰的通道使人可以在11000-18000这段时间到达这里。

C：某证据显示人不可能在18500年前到达这里。（那么18000-18500之间呢？如果人能来了，不就是支持结论了吗？）

題目說那段時間沒有人可以進出那個區域, 因為冰天雪地

C說 that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge

就是在兔槽說 其實有一條沒有結冰的corridor (走廊) 可以走

自然就反擊了之前胡扯說 不能穿越該地區的結論