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': "Starling's law of the heart \nSelect and explain. \nA. Does not operate in the failing heart, B. Does not operate during exercise, C. Explains the increase in cardiac output that occurs when venous return is increased, D. Explains the increase in cardiac output when the sympathetic nerves supplying the heart stimulated", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]