This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Fouh hea sound is caused by 
Select and explain. 
A. Closure of AV valves, B. Closure of semilunar valves, C. Rapid ventricular filling, D. Atrial contraction
D: Atrial contraction
Answer: D: Atrial contraction 
Explanation: A fouh sound can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hyperophy. It is due to ventricular filling and is rarely heard in normal adults.Ref: Ganong&;s Review of medical physiology 25th edition. Page: 542