Question

external respiration refers to the exchange of oxygen and carbon dioxide between the:
a alveoli and bloodstream.
b outside air and cells of the body.
c bloodstream and cells.
d lungs and heart.

Explanation:

External respiration is the gas - exchange process between the alveoli in the lungs and the bloodstream. Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli.

Answer:

A. alveoli and bloodstream