Which type of blood vessel contains valves to prevent backflow?

• A. Veins.
• B. Arteries.
• C. Capillaries.
• D. Lymph Ducts.

Answer: (D)

Valves prevent backflow in vessels that carry blood back to the heart under low pressure, helping maintain one-way flow. Veins have one-way valves, especially in the limbs, to stop blood from pooling as it returns to the heart. Arteries carry blood away from the heart at high pressure, so they don’t need valves. Capillaries are tiny exchange vessels with no room for valves. Lymph ducts belong to the lymphatic system and do have valves, but they are not blood vessels. Since the question is about blood vessels, the structure with valves is veins.