Calcium is an important part of a healthy diet. Which of the following occurs if the levels of calcium in
the blood fall below normal?
a. Parathyroid hormone and calcitonin levels increase.
b. Parathyroid hormone and calcitonin levels decrease.
c. Parathyroid hormone levels increase and calcitonin levels decrease.
d. Parathyroid hormone levels decrease and calcitonin levels increase.