Correct Option: A

Human heart has four valves: two atrioventricular (AV) valves, which are between the atria and the ventricles, are the mitral valve and the tricuspid valve; and two semilunar (SL) valves, which are in the arteries leaving the heart, are the aortic valve and the pulmonary valve. A heart valve normally allows blood flow in only one direction through the heart.