(ii) If the blood is no longer under high pressure in veins, how do they avoid the back flow of blood?
(a) There is sufficient pressure for the blood to flow in one direction.
(b) There are special organs in veins which pump blood towards the heart.
(c) There are valves in the veins which prevent the back flow of blood.
(d) The blood does not flow in one direction. It flows by gravity.
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Answer:
A
Explanation:
A because pressure of blood flow only one same direction
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