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': "What is the effect of sleep on cardiac output? \nSelect and explain. \nA. Cardiac output increases, B. Cardiac output decreases, C. Cardiac output remains same, D. Can't say", 'role': 'user'}, {'content': 'Answer: C \nExplanation: No change in Cardiac output occurs during sleep.', 'role': 'assistant'}]