A. Thyroid
B. Parathyroid
C. Adrenal medulla
D. A and B
Explanation:
The parathyroid glands are a group of four glands neighboring the thyroid gland that are the main regulators of the blood calcium in your body (See Parathyroid Glands-Illustration). Parathyroid glands release parathyroid hormone (PTH) which increases your blood calcium levels.