23. Which one of the following statements is NOT true for the mammalian circulation system?
(A) Both arteries and veins have an endothelium, smooth muscle, and connective tissue.
(B) Both arteries and veins contain valves to maintain unidirectional blood flow.
(C) Blood flow in capillaries is necessarily slow for exchange of materials.
(D) The recoil of elastic arterial walls plays a role in maintaining blood pressure.
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