Easy, I learned this last year.
Early, as humans, we were known as hunter-gatherers, where we pursued our food. We would follow the food wherever it went.
Imagine, you're hungry, but you're food is moving somewhere;obviously you'd pursue it to eat.
Thus, your answer is A, Hunters pursued their prey across a land bridge into the Americas.
They followed the food, but that land bridge "disappeared" most likely swallowed up by the sea.