Question

fill in the blank question
veins have
that ensure the one way flow of blood.
need help? review these concept resources.

Explanation:

In the circulatory system, veins are responsible for carrying blood back to the heart. To ensure that blood flows in only one direction (towards the heart) and doesn't backflow, veins contain valves. These valves open to allow blood to move forward and close to prevent it from flowing backward.

Answer:

valves