Livestock Owners and Breeders Have Most Likely Maximized Their Abilities

Livestock owners and breeders have most likely maximized their abilities to greatly improve size and speed of the animals that they raise.This is a consequence of

A) too many crossing over events in previous livestock generations.
B) not enough crossing over events in previous livestock generations.
C) existing genetic combinations have been nearly exhausted as well as the limited amount of genetic variability that existed to begin with.
D) using artificial insemination instead of allowing animals to breed on their own.