Which statement correctly describes arterial-venous oxygen transport?

• A. Artery carries deoxygenated blood away from the heart; Vein carries oxygenated blood to the heart.
• B. Artery carries oxygenated blood to the heart; Vein carries deoxygenated blood away.
• C. Artery exchanges gases with tissues; Vein regulates blood flow.
• D. Artery carries oxygenated blood away from the heart; Vein carries deoxygenated blood to the heart.

Answer: (D)

The main idea is how oxygen is carried by the vessels as blood moves through the body. In systemic circulation, arteries carry oxygen-rich blood away from the heart so that tissues receive the oxygen they need, while veins return blood with lower oxygen content back to the heart. This direction and oxygen content align with normal physiology: the left heart pumps oxygenated blood into the arteries, oxygen is delivered at the capillary beds, and deoxygenated blood returns via veins to the right heart. A useful nuance is that in the pulmonary circuit the pattern reverses because blood is oxygenated in the lungs—pulmonary arteries carry relatively deoxygenated blood away from the heart to the lungs, and pulmonary veins bring oxygenated blood back to the heart. The described statement matches the systemic pattern, while the other descriptions mix up oxygen content, wrong routes, or assign gas exchange to larger vessels rather than capillaries.