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
Which of the following is the most common cause of midsystolic murmur in adults? 
Select and explain. 
A. Aortic stenosis, B. Aortic regurgitation, C. Hypertrophic obstructive cardiac myopathy, D. All of the above
A: Aortic stenosis
Answer: A: Aortic stenosis 
Explanation: AS is the most common cause of a midsystolic murmur in an adult.