What did the disappearance of the Bering Land Bridge mean for further

What did the disappearance of the Bering Land Bridge mean for further human migration from Alaska to the southern tip of South America?

A) Any further migration from Alaska to South America had to be by boat.
B) Any further migration from Alaska to South America had to occur much later than 14,000 years ago.
C) Any further migration from Alaska to South America had to be created by the development of a mini-Ice Age permitting another land bridge from North America to South America.
D) This disappearance of the Bering Land Bridge had no implications for further migration from Alaska to the southern tip of South America.

ANSWER
Answer: A