B
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
Arteries and veins are two important parts of the circulatory system. What is the relationship between arteries and veins?

### Choices:
A. They work together to exchange gases.
B. They work together to transport nutrients.
C. They work independently to remove wastes.
D. They work independently to relay messages.

### Answer:
