Which of the following represents the correct sequence of parts through which blood moves in passing from the vena cava to the lungs?
a. right atrium, pulmonary semilunar valve, right ventricle, tricuspid valve
b. right atrium, tricuspid valve, right ventricle, pulmonary semilunar valve
c. tricuspid valve, right atrium, pulmonary semilunar valve, right ventricle
d. pulmonary semilunar valve, right atrium, tricuspid valve, right ventricle