As the years increase the deer population increases.
As the years increase the the wolf decreases
I'm not sure how exactly you wanted this question to be answered. You're either talking about the symmetry where animals would have two legs or two arms for example and thus producing a pair of each muscle on both sides of the body, or you're refering to the development of agonistic and antaonistic muscles where each of them served a different purpose; either extending or contracting.
Answer should be A if multiple choice
Answer:
STEM CELLS
They serve as a repair system for the body.
