Which one of the following valves guards the opening between the right ventricle and the pulmonary artery?

The opening between the right ventricle and the pulmonary artery is guarded by the pulmonary semilunar valve, which prevents backflow of blood from the pulmonary trunk into the right ventricle during diastole. The tricuspid valve lies between the right atrium and right ventricle. The bicuspid (mitral) valve lies between the left atrium and left ventricle. Aortic semilunar valve guards the opening between the left ventricle and the aorta. Hence the answer is the semilunar valve.