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The first heart sound ('lub') is produced by

AClosure of pulmonary and aortic valves
BOpening of tricuspid and bicuspid valves
COpening of pulmonary and aortic valves
DClosure of tricuspid and bicuspid valves
Answer & Solution
Correct answer: D. Closure of tricuspid and bicuspid valves
'Lub' = closure of atrioventricular valves (tricuspid right, bicuspid/mitral left) at the start of ventricular systole. 'Dub' = closure of semilunar valves (pulmonary and aortic) at the end of ventricular systole.
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