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': 'First hea sound is soft in all, except: \nSelect and explain. \nA. Sho PR interval, B. Ventricular septal defect, C. Mitral regurgitation, D. Calcified valve', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer is A (Sho PR interval) Sho PR interval is associated with a Loud S,. SI is produced as a result of closure of AV valves. In sho PR interval mitral leaflets are at a greater distance from neutral as decreased interval between atrial contraction and ventricular systole does not allow them to return towards neutral before the ventricular contraction', 'role': 'assistant'}]