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': 'Duration of 2nd heart sound is: \nSelect and explain. \nA. 0.15 sec, B. 0.12 sec, C. 0.08 sec, D. 0.1 sec', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Second heart sound duration is 0.1 to 0.14 sec (average 0.12 sec).', 'role': 'assistant'}]