The correct option is D Parathyroid
The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. Parathyroid hormone (PTH, also know as parathormone) is a small protein that takes part in the control of calcium and phosphorus homeostasis, as well as bone physiology. When blood calcium level drops below a certain point, calcium – sensing receptors in the parathyroid gland are activated to release hormone into the blood. It then stimulates osteoclasts to break down bone and release calcium into the blood, and increase gastrointestinal calcium absorption.