Name a difference between a vein and artery

Arteries like veins, are tube-shaped vessels that carry blood in the body. 
But the difference is that the artery carries oxygenated blood away from the heart to the body. But the veins carry poor-oxygen blood back from the body to the heart! 
I hope this helps! :)

Arteries carry oxgenated blood away from the heart to the rest of the body. They have thick elastic walls to withstand high blood pressure being pumped from the blood. This is why they appear red in colour.

On the other hand, veins carry deoxygenated blood back to the heart. They are thin in comparison to the artery, as they are under lower blood pressure. However, veins contain valves to prevent backflow of blood as veins carry deoxygenated blood.

The correct answer is "b"

Sorry  i don't understand can you rephrase that