Final answer:
The factor that most likely facilitated large-scale human migration from Asia to North America during the prehistoric age is the emergence of a land bridge during climate change.
Step-by-step explanation:
The factor that most likely made large-scale human migration from Asia to North America possible during the prehistoric age is D) A land bridge emerged during climate change.
During the last ice age, a land bridge called Beringia emerged between modern-day Alaska and Russia due to lower sea levels. This land bridge provided a physical connection between Asia and North America, allowing humans to cross from one continent to the other on foot.
Archaeological evidence suggests that humans migrated from Siberia to Alaska across the Bering Land Bridge around 14,000-20,000 years ago. This migration was made possible by the drop in sea levels as massive glaciers formed, revealing the land bridge.