Which of the following statements on the mammalian circulatory system is NOT true?

• A.Blood in the pulimonary artery is richer in oxygen content than blood in the pulmonary vein
• B.The blood in the hepatic portal vein is the richest in food substance
• C.Blood flow is controlled by valves in the veins
• D.Arteries are generally thicker and larger than veins
• E.Fibrin helps in the formation of blood clot