The correct option is A Oxytocin
The baby's sucking stimulates nerve endings in the nipple, which signal the mother's pituitary gland to release oxytocin, a hormone that causes the mammary glands to release milk to the nursing baby. This is called as the "let-down reflex." While the baby's sucking is the primary stimulus for this reflex, a baby's cry, thoughts of the baby also may trigger the response.