Answer:Veins. I hope this helps you
Step-by-step explanation:
Veins are the blood vessels that contain valves to prevent blood from flowing backwards. The valves in veins allow blood to flow towards the heart, but prevent it from flowing backwards due to gravity or pressure changes.
Veins are blood vessels that are part of the circulatory system. They are responsible for carrying blood back to the heart after it has circulated throughout the body. Veins are characterized by their thin walls and valves that prevent backflow of blood. They are usually located deeper in the body than arteries, and appear blue or green in color due to the way that light is absorbed and reflected through the skin.