Question

question 3 external respiration refers to the exchange of oxygen and carbon dioxide between: outside air and cells of the body, bloodstream and cells, alveoli and bloodstream, lungs and heart

Explanation:

External respiration is the gas - exchange process where oxygen from the outside air enters the bloodstream and carbon dioxide leaves the bloodstream to the outside air. It occurs between the outside air and the blood in the lungs. This gas exchange takes place across the alveoli and the bloodstream.

Answer:

B. alveoli and bloodstream