Final answer:
The correct answer is D. mitral; aortic, where the mitral valve closes to prevent backflow of blood into the left atrium, and the aortic valve opens to allow blood to flow from the left ventricle into the aorta.
Step-by-step explanation:
When the left ventricle contracts, the mitral valve closes and the aortic valve is pushed open. Therefore, the correct answer to the question is D. mitral; aortic.
The mitral valve, also known as the bicuspid valve, is an atrioventricular valve that separates the left atrium from the left ventricle. Its closure prevents the backflow of blood into the left atrium. The aortic valve is a semilunar valve that allows blood to be ejected from the left ventricle into the aorta, the main artery that carries oxygen-rich blood to the body. This process is an essential part of the double circulation found in mammals and ensures that oxygenated blood is efficiently distributed throughout the body.