The correct answer is C. 20K years ago.
Step-by-step explanation
The border sector between the current United States and Russia in the Bering Strait is a geological formation that separates Asia and America with 82.7 km of sea. Scientists have accepted the theory that states that the first settlers of America crossed through this sector about 20K years ago, with the help of an ice bridge product of the ice ages that existed on earth at that time. In this way, primitive nomadic communities crossed into what is now known as America and from there they populated the entire continent. Therefore, the correct answer is C. 20K years ago.