This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
[{'content': 'Milk ejection reflex is mediated by the hormone: \nSelect and explain. \nA. Oxytocin, B. Vasopressin, C. Growth hormone, D. Thyroxin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A', 'role': 'assistant'}]