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
The third heart sound is due to: 
Select and explain. 
A. Closure of AV valve, B. Closure of aortic valve, C. Mid diastolic flow in the ventricle, D. Atrial contraction
C: Mid diastolic flow in the ventricle
Answer: C: Mid diastolic flow in the ventricle 
Explanation: “A  soft, low-pitched  third sound  is heard about one third of the way through diastole in many normal young individuals.”