Which of the following statements correctly describes how parathyroid hormone regulates bone deposition and reabsorption?
a. Parathyroid hormone tells osteoclasts to reabsorb bone resulting in increased blood calcium levels
b. Parathyroid hormone is produced when blood calcium levels are high.
c. Parathyroid hormone tells osteoblasts to deposit calcium in the bone.
d. Parathyroid hormone is produced when blood calcium levels are low.