They work together to exchange gases. They work together to transport nutrients. They work independently to remove wastes. They work independently to relay messages.
I gave my students this multiple choice question: Arteries and veins are two important parts of the circulatory system. What is the relationship between arteries and veins?

Only one answer is correct among these 4 choices:
- They work together to exchange gases.
- They work together to transport nutrients.
- They work independently to remove wastes.
- They work independently to relay messages.

Could you tell me which one is correct?

They work together to transport nutrients.