Final answer:
The valve between the right atrium and the right ventricle is the A. tricuspid valve, which is an atrioventricular valve found on the right side of the heart.
Step-by-step explanation:
The valve between the right atrium and right ventricle is the tricuspid valve. This is also known as an atrioventricular valve, which is a one-way valve located between the atria and ventricles. The tricuspid valve consists of three flaps of tissue that prevent backflow of blood from the right ventricle back into the right atrium. The bicuspid (mitral) valve, also an atrioventricular valve, is found between the left atrium and ventricle, not the right side of the heart. In contrast, semilunar valves, specifically the aortic and pulmonary valves, are situated at the base of the aorta and the pulmonary artery, respectively. Therefore, the correct answer to the question is A. tricuspid valve.