When blood calcium levels are high, ____ is released from the thyroid gland to deposit the excess calcium into the bones.
Correct Answer: B
Rationale: Calcitonin is the correct answer because it is released from the thyroid gland in response to high blood calcium levels to deposit the excess calcium into the bones, decreasing blood calcium levels. Parathyroid hormone (A) works in the opposite way, increasing blood calcium levels by releasing calcium from bones. Oxytocin (C) is a hormone involved in labor and breastfeeding, not calcium regulation. Glucagon (D) is released from the pancreas to increase blood glucose levels, not calcium levels. Therefore, calcitonin is the most suitable choice for regulating high blood calcium levels by promoting calcium deposition in the bones.