The first heart sound (lub) is produced by the closing of the ____ and ____ valves

a. aortic semilunar; pulmonary semilunar
b. right atrioventricular; aortic semilunar
c. left atrioventricular; pulmonary semilunar
d. right atrioventricular; left atrioventricular
e. mitral; left atrioventricular


d

Biology & Microbiology

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Which of the following is/are TRUE regarding serotonin?

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