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: Medicine
[{'content': 'All of the following heart sounds occur shortly after S2 except \nSelect and explain. \nA. Opening snap, B. Pericardial knock, C. Ejection click, D. Tumor plop', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]