Question

question 15 (2 points) listen alveoli are never damaged by pollution or disease the primary site of gas exchange between the air in the lungs and the circulatory system all of these are correct responsible for the immune defense of the respiratory system composed of two layers of smooth muscle approximately 200 in number in each lung

Explanation:

Alveoli are tiny air - sacs in the lungs. They are the primary site of gas exchange between the air in the lungs and the circulatory system. They can be damaged by pollution and diseases, are not responsible for immune defense of the respiratory system, are not composed of two layers of smooth muscle, and there are far more than 200 in each lung.

Answer:

the primary site of gas exchange between the air in the lungs and the circulatory system