By age 20, a person's bones stop growing
a. bone-forming cells are no longer present.
b. less calcium is present in the body.
c. hormones cause the growth centers at the ends of the bones to degenerate.
d. bone cells receive less oxygen and nutrients at that time.

By age 20, a person's bones stop growing because hormones cause the growth centers at the ends of the bones to degenerate. The correct option among all the options that are given in the question is the third option or option "C". I hope that the answer has come to your help.

It really hasn't, but teens no longer smoke cigarettes, because now the some weed so there's actually no need to buy cigarettes. hope I helped