Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Arteries and veins are two important parts of the circulatory system. What is the relationship between arteries and veins?
They work together to transport nutrients.
Arteries carry blood away from the heart, while veins carry blood back to the heart.