This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Which is true about heart sound? 
Select and explain. 
A. First heart sound has maximum frequency, B. First heart sound has maximum duration, C. First heart sound is due to semilunar valve closure, D. Second heart sound is due to AV valve closure
B: First heart sound has maximum duration
Answer: B: First heart sound has maximum duration 
Explanation: Ans. B First heart sound has maximum durationHeart soundFrequencyDurationAssociated eventFirst heart25-45 Hz0.15 secClosure of A-V valves--onset of ventricular systoleSecond heart sound50 Hz0.12 secClosure of semilunar valves--onset of ventricular diastoleThird heart soundLow0.1 secFirst rapid filling phase of ventricular diastoleFourth heart soundBelow 20 Hz0.1 secLast rapid filling phase of ventricular diastole due to atrial contraction