Question

melatonin is produced by the ______.
pituitary gland
thymus gland
pineal gland
heart

Explanation:

Melatonin is a hormone that regulates sleep - wake cycles. The pineal gland is responsible for producing melatonin. The pituitary gland has various functions like regulating other endocrine glands but not melatonin production. The thymus gland is involved in the immune system and T - cell development. The heart is a muscular organ for pumping blood and not involved in melatonin production.

Answer:

C. pineal gland