The Faster a Cheetah Can Run, the More Likely It

The faster a cheetah can run, the more likely it is to capture its prey. Cheetahs with longer legs are able to run faster than those with shorter legs. Although the existing cheetah population shows a variety of leg lengths, cheetah legs are not continuing to increase in length from one generation to the next. Which of the following is a possible explanation?

A) The genes that are involved in cheetah leg length do not undergo mutation.
B) Cheetahs with long legs are reproductively isolated from cheetahs with short legs.
C) Natural selection does not act on traits involved in predation.
D) Longer cheetah leg bones are more likely to break.