Explain the mechanism producing normal first and second heart sounds?
a) The closure of the atrioventricular valves produces the first heart sound (S1), while the closure of the semilunar valves produces the second heart sound (S2).
b) The opening of the atrioventricular valves produces the first heart sound (S1), while the opening of the semilunar valves produces the second heart sound (S2).
c) The contraction of the atria produces the first heart sound (S1), while the contraction of the ventricles produces the second heart sound (S2).
d) The relaxation of the atria produces the first heart sound (S1), while the relaxation of the ventricles produces the second heart sound (S2).
