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
2nd hea sound is due to 
Select and explain. 
A. Closure of AV valves, B. Closure of aoic valve, C. Inthrushing of blood, D. Atrial contraction
B: Closure of aoic valve
Answer: B: Closure of aoic valve 
Explanation: The second is a shoer, high-pitched "dup" (second sound), caused by vibrations associated with the closure of the aoic and pulmonary valves just after the end of ventricular systole.Ref: Ganong&;s Review of medical physiology 25th edition. Page: 542