Fact 1: Smoking causes direct damage to the lungs.

Fact 2: With emphysema, there is permanent lung damage in the alveoli.

Given the two facts above, answer the question "Emphysema can be caused by" with the following options: 
- Pollution
 - nitric oxide
 - smoking
 - steroids
 - Pesticides
 - pollen
 - hormones
 - hydrogen peroxide


 

   smoking      