They both bring oxygen to the body. They both send messages to the body. They both digest nutrients for the body. They both pump blood through the body.
I gave my students this multiple choice question: Kendall studied the ways in which human body systems work together. He compared the respiratory and circulatory systems. In which way are these two systems similar to each other?

Only one answer is correct among these 4 choices:
- They both bring oxygen to the body.
- They both send messages to the body.
- They both digest nutrients for the body.
- They both pump blood through the body.

Could you tell me which one is correct?

They both bring oxygen to the body.