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
Loud S1 is caused by- 
Select and explain. 
A. Calcified mitral valve, B. Mitral Regurgitation, C. Sho PR interval, D. Bradycardia
C: Sho PR interval
Answer: C: Sho PR interval 
Explanation: 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