The correct option is D Parathormone
When blood calcium levels drop, the parathyroid gland secretes parathyroid hormone. This hormone works to raise blood calcium levels by stimulating osteoclasts to break down bone and release calcium into the blood stream. PTH also signals kidneys to conserve calcium by reducing the amount excreted in the urine.The hormone also stimulates kidney production of the active form of vitamin D, which triggers increased calcium absorption from the gut.