To solve this problem, we need to understand why the alveoli in the lungs do not collapse even after forceful expiration.$\newline$Let's analyze the options:$\newline \bullet$Inspiratory reserve volume:$\newline$ - This is the additional volume of air that can be inhaled after a normal inhalation.$\newline$ - It does not prevent alveolar collapse after expiration.$\newline \bullet$Tidal volume:$\newline$ - This is the volume of air inhaled or exhaled during a normal breath.$\newline$ - It is not related to preventing alveolar collapse after forceful expiration.$\newline \bullet$Expiratory reserve volume:$\newline$ - This is the additional volume of air that can be exhaled after a normal exhalation.$\newline$ - It does not prevent alveolar collapse after forceful expiration.$\newline \bullet$Residual volume:$\newline$ - This is the volume of air remaining in the lungs after a forceful expiration.$\newline$ - It prevents the alveoli from collapsing by maintaining a certain amount of air in the lungs.$\newline$Therefore, the correct answer is that the alveoli do not collapse after forceful expiration because of the residual volume.$\newline$This corresponds to Option 4.