Answer the following question given this paragraph: 

Emphysema is a disease in which the walls of the alveoli break down so less gas can be exchanged by the lungs. The main symptom of emphysema is shortness of breath. The damage to the alveoli is usually caused by smoking and is permanent.


Q: What disease associated with smoking involves breakdown of walls of the alveoli, resulting in less gas exchange by the lungs?


A:
emphysema