Lungs are made of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of: A. Inspiratory Reserve Volume B. Tidal volume C. Expiratory Reserve Volume D. Residual Volume
Option D. Residual Volume (RV) is the volume of air remaining in the lungs even after a forcible expiration. This is main reason why alveoli do not collapse even after forceful expiration.
