Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins?

Most veins are equipped with valves to prevent regurgitation (reverse blood flow). The return of blood to the heart is assisted by the action of the skeletal-muscle pump, and by the thoracic pump action of breathing during respiration.

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Ithink that b is correct but just in case wait to see if someone else answers

I’m not exactly sure what your trying to ask, but if it’s how an organelle is similar to a body system or a part a nucleus is like a in function. but i don’t fully understand what you’re trying to ask