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Which event produces the first heart sound, called lub?

AClosing the atrioventricular valves
BOpening the semilunar valves
CClosing the semilunar valves
DOpening the atrioventricular valves
Answer & Solution
Correct answer: A. Closing the atrioventricular valves
The first heart sound accompanies closure of the tricuspid and bicuspid valves.
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