Which statement correctly describes the structural and functional characteristics of arteries, veins, and capillaries?

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The key idea is that the structure of each vessel type is matched to its job in circulation. Arteries carry blood away from the heart under high pressure, so they have thick walls with a prominent muscular layer (the tunica media) and elastic fibers. This design lets them withstand the surge of blood with each heartbeat and helps propel blood forward.

Veins return blood to the heart at lower pressure, so their walls are thinner and their lumens wider. They also house valves that prevent backflow, which is especially important as blood pools in the lower parts of the body and must move against gravity toward the heart.

Capillaries are the sites of exchange, so they are extremely thin—usually just a single endothelial cell layer. This thin wall, with a tiny diameter, maximizes diffusion of oxygen, carbon dioxide, nutrients, and wastes between blood and tissues.

Therefore, the statement that arteries carry blood away from the heart with thick muscular walls; veins return blood to the heart with valves; capillaries are thin-walled for exchange accurately describes both structure and function. The other ideas are inconsistent with what each vessel type is built to do: arteries don’t carry blood toward the heart and aren’t thin-walled, veins do have valves, and capillaries aren’t thick-walled.