Read the following summary, which describes a body process. Then answer the question Air enters the nasal cavity. It goes into the pharynx and moves into the trachea. Air enters the right and left bronchus, where it is then delivered to the lungs. After air enters the alveoli, oxygen moves through the wall of the alveoli and into the blood. Then carbon dioxide and water pass from the blood out into the air through the alveoli, also.

What process is being described?

A. Circulation

B. Excretion

C. Immune response

D. Respiration