This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Role of calcitonin is: \nSelect and explain. \nA. Lower Ca level, B. Increase Ca level, C. Decrease PO4, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Lower Ca level', 'role': 'assistant'}]