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': 'The third heart sound is due to: \nSelect and explain. \nA. Closure of AV valve, B. Closure of aortic valve, C. Mid diastolic flow in the ventricle, D. Atrial contraction', 'role': 'user'}, {'content': 'Answer: C \nExplanation: “A\xa0 soft,\xa0low-pitched\xa0 third\xa0sound\xa0 is\xa0heard about one third of the way through diastole\xa0in many normal young individuals.”', 'role': 'assistant'}]