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
Which physical sign characterizes mitral stenosis: 
Select and explain. 
A. Loud first heart sound, B. Soft single second heart sound, C. Third heart sound, D. Pulsatile liver
A: Loud first heart sound
Answer: A: Loud first heart sound 
Explanation: None