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': 'Which of the following is the most common cause of midsystolic murmur in adults? \nSelect and explain. \nA. Aortic stenosis, B. Aortic regurgitation, C. Hypertrophic obstructive cardiac myopathy, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: AS is the most common cause of a midsystolic murmur in an adult.', 'role': 'assistant'}]