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': 'Normally, the rate of the heart beat in a human is determined by: \nSelect and explain. \nA. The bundle of His, B. All cardiac muscle, C. The sinoatrial node, D. The cervical ganglion', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]