What causes venous blood to return to the heart? A. The pumping action of the heart. B. The squashing action of muscles, and valves in the veins. C. Rhythmic vasoconstriction and valves in the veins. D. Gravity, valves and the negative pressure generated by the atria emptying.
Option B. Valves prevents blood in veins from flowin from the heart, even as contracting skeletal muscle compresses the veins and this pushes blood thru them closer to the heart (because the valves prevent blood formed being pushed withinside the different direction.
