Which one of the following is true concerning the lub-dub sounds of the heart:
A) the first sound is longer and louder and is caused by closure of the tricuspid valve; the second sound is shorter and sharper and is caused by closure of the mitral valve
B) the first sound is shorter and sharper and is caused by closure of the tricuspid valve; the second sound is longer and louder and is caused by closure of the mitral valve
C) they are caused by contraction of the ventricles, followed by contraction of the atria
D) the first sound is longer and louder and is caused by closure of the AV valves; the second sound is shorter and sharper and is caused by closure of the semilunar valves
E) the first sound is shorter and sharper and is caused by closure of the semilunar valves; the second sound is longer and louder and is caused by closure of the AV valves
Answer: D