Answer:
The correct option is: a. parathyroid hormone (PTH)
Step-by-step explanation:
Parathyroid hormone is a hormone secreted by the chief cells of the parathyroid gland. Parathyroid hormone, abbreviation PTH, is secreted when the blood calcium ion levels are low. This hormone stimulates the osteoclast activity in the bone matrix, indirectly, to increase the concentration of calcium ions in the blood.