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': 'Loud S1 is caused by- \nSelect and explain. \nA. Calcified mitral valve, B. Mitral Regurgitation, C. Sho PR interval, D. Bradycardia', 'role': 'user'}, {'content': "Answer: C \nExplanation: Loud S1: Tachycardia Sho PR Interval. Mitral stenosis Tricuspid stenosis Soft S1: Bradycardia Prolonged PR Interval Aoic regurgitation Pulmonary regurgitation. Ref : Harrison's 20th edition pg 1563", 'role': 'assistant'}]