Many Lines of Evidence Suggest That Human Populations Aren't Distinct

Multiple Choice

Many lines of evidence suggest that human populations aren't distinct races. Why are we so similar even though adaptations to local conditions have occurred?

A) Members of different populations mate with each other.
B) Natural selection has acted in the same way for all groups of humans.
C) Populations mate assortatively.
D) Sexual selection has acted in the same way for all groups.