A) Closure of atrioventricular valves
B) Opening of atrioventricular valves
C) Closure of semilunar valves
D) Thrust of blood on ventricular wall during atrial contraction
Correct Answer: C
Solution :
The first heart sound Lubb is produced at the onset of ventricular systole, when the atrio-ventricular valves (tricuspid and bicuspid) close. At the beginning of ventricular diastole, the semilunar valves close, producing the second heart sound dup.
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