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
[{'content': 'S2 is associated with ? \nSelect and explain. \nA. Rapid ventricular filling, B. Atrial contraction, C. Closure of semilunar valves, D. Closure of AV valves', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Closure of semilunar valves", 'role': 'assistant'}]