The correct option is B Parathyroid
Parathyroid hormone (PTH, also known as parathormone) takes part in the control of calcium and phosphorus homeostasis as well as bone physiology. PTH is synthesized and released in response to falling levels of Ca++ in the blood. PTH stimulates the osteoclasts (bone cells) in the bone to dissolve the calcium phosphate crystals of the bone matrix and release Ca++ into the blood. PTH also stimulates the kidneys to reabsorb Ca++ from the urine and leads to the activation of vitamin D, needed for the absorption of Ca++ from food in the intestine. Thus, any malfunctioning of the parathyroid gland results in problems with calcium levels.