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
The fouh hea sound is caused by? 
Select and explain. 
A. Closureiof the aoic and pulmonary valves, B. Vibrations inihe ventricular wall during systole, C. Ventricula filling, D. Closure of the mitral and tricuspid valves
C: Ventricula filling
Answer: C: Ventricula filling 
Explanation: A fouh hea sound is common in persons who derive benefit from atrial contraction for ventricular filling as a result of decreased ventricular wall compliance and increased resistance to ventricular filling. For example, a fouh hea sound is often heard in older patients with left ventricular hyperophy.Ref: Guyton and Hall textbook of medical physiology 13th edition. Page:284