Please Read the Following Scenario to Answer the Following Questions

Please read the following scenario to answer the following questions.
Osteoporosis is a disease characterized by loss of bone mass and an increased susceptibility to bone fractures.It threatens more than half of all Americans over the age of 50.Women are about four times more likely to suffer from the disease than men.Osteoporosis may progress undetected until bones become so weak that they break during common activities.Prevention of osteoporosis includes regular weight-bearing exercise,recommended intake of calcium and vitamin D,and avoidance of smoking and excessive alcohol.
-Calcium levels are regulated by antagonistic hormones.This is likely because ________.

A) calcium has to be produced by the body and that production must be regulated
B) bone formation occurs only during puberty when many other hormones are present,thus careful regulation is necessary
C) both too much and too little calcium can have disastrous effects on the body,thus the levels need tight regulation
D) calcium is needed to repair bone fractures,so antagonistic hormones make sure it is available when needed