Respuesta :

hannahashscott

Answer:

External respiration is the exchange of gases with the external environment, and occurs in the alveoli of the lungs.
The alveoli are where the lungs and the blood exchange oxygen and carbon dioxide during the process of breathing in and breathing out. External Respiration. Exchange of gases between air and blood at pulmonary capillaries (Alveoli) is the second stage. So it would be the 2nd stage