The heart and veins have valves to ensure that.A. Blood flow in only one direction.B. Oxygen and carbon dioxide can be exchanged.C. Lymph can be directed through arteries.D. Platelets do not clot at the site of the wound.
The heart and veins have valves to ensure that the blood flow goes in one direction and thus prevent oxygenated blood from mixing with carbo oxygenated blood. (option A).
