In Theory, a Biological Race Is a Geographically Isolated Subdivision

In theory, a biological race is a geographically isolated subdivision of a species. Humanity (Homo sapiens) lacks such races because

A) although humans exhibit biological differences, these are only skin deep.
B) humans are less genetically predictable than animals and plants susceptible to domestication.
C) human populations have not been isolated enough from one another to develop such discrete groups.
D) human populations have experienced a type of controlled breeding distinct from that of dogs and roses.
E) they are politically incorrect.