This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
[{'content': 'The severity of mitral stenosis is assessed by \nSelect and explain. \nA. Character of murmur, B. Splitting of S, C. Loudness of S,, D. S2-OS interval', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Mitral stenosis. A normal mitral valve will have an area of >4 cm2, but symptoms are usually only present once the stenosis is moderate-severe. Grading into mild, moderate, or severe disease is based on both the pressure needed to drive blood across the valve (mean pressure gradient) and the valve area. Ref Davidson 23rd edition pg 435', 'role': 'assistant'}]