URGENT!!!!! HELP! LIMITED TIME!!!!!!!!!!!!

Scientists discover two populations of mice on either side of a major river.

The two populations have almost identical genes, but the mice from one side cannot breed with the mice from the other.
This is most likely because

Select one:

A. both species of mice lived on both sides but owls killed one
population on each side

B. the river separated one species of mice into two different species.

C. the similar habitat caused two species to become genetically
similar

D. two different species of mice migrated to the river from different directions