Myostatin Mutations That Increase Muscle Mass May Not Be Favored

Myostatin mutations that increase muscle mass may not be favored by evolution because

A) larger muscles in animals that have impaired myostatin production actually produce less force than normal muscles.
B) larger muscles fatigue more rapidly in myostatin-null animals.
C) impaired atrophy may deprive myostatin-null animals of the amino acids needed for physiological processes in non-muscle tissues.
D) the high degree of conservation of the myostatin sequence in different tetrapods indicates that the gene is not important in most animals.