Circulatory and respiratory systems work together to circulate blood and oxygen throughout the body. Which of the following is the function of respiratory system?

A. Breaking down food for it be used by the body.
B. Holding up the body and giving it support and shape.
C. Gas exchange between the external environment and the body’s circulatory system.
D. Sweep mucus with its trapped particles up and out of the body to avoid illness.​