Question 7:

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What is the meaning of the bold word as it is used in the sentence?
While arteries move blood away from the heart, veins bring it back to the heart. Each vein has a valve to prevent blood from moving in a reverse pattern.

A chemical that exists in the blood

Something that prevents a liquid from becoming solid

An organ that functions adequately

Something that controls the flow of liquid through a tube

Something that controls the flow of liquid through a tube