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
Pansystolic murmur at apex with soft first heart sound is the key sign of which one of the following ? 
Select and explain. 
A. Aortic regurgitation, B. Mitral regurgitation, C. Ventricular septal defect, D. Atrial septal defect
B: Mitral regurgitation
Answer: B: Mitral regurgitation 
Explanation: None