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': 'The severity of Mitral stenosis is clinically best decided by - \nSelect and explain. \nA. Length of diastolic murmur, B. Intensity of diastolic murmur, C. Loudness of first heart sound, D. Split of second heart sound', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]