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: Physiology
S2 is associated with ? 
Select and explain. 
A. Rapid ventricular filling, B. Atrial contraction, C. Closure of semilunar valves, D. Closure of AV valves
C: Closure of semilunar valves
Answer: C: Closure of semilunar valves 
Explanation: Ans. is 'c' i.e., Closure of semilunar valves