posted by susue .
blood flow is maintained in the veins by?
B.valves in the veins which prevent back-flow
C.muscular pumping action of the vein walls
D.partial vacuum in the heart
my answer is b
Veins carry blood back to the heart. the blood in them is at low pressure. thus, the wall of a vein is not as thick, muscular or elastic as than that of an artery of about the same size. Most veins have valves inside them to prevent back flow of blood. the flow of blood along veins is assisted by the movements of the skeletal muscle.
Answer A is wrong,mainly. C is wrong, as vein walls have no muscles. D is ridiculous. B is probably the best choice, but it is incomplete.