GWD-11-41

billion

答案：B

原文结论："humans must have come to the Americas more than 18,000 years ago."

The Americas (用google查的）
(sometimes referred to as America) is the area including the land mass located between the Pacific Ocean and the Atlantic Ocean, generally divided into North America and South America. The term also usually includes the Caribbean, the islands in and around the Caribbean Sea, and Greenland, though not Iceland, for cultural and historical reasons. The isthmus of Central America is usually considered geographically part of North America. The Americas are often also described collect...

所有人都应该知道new mexico是美洲大陆的一部分，在该处发现"remains dated at 16,000 years old"的证据，完全可以削弱原文结论。