You are presented with the question "Emphysema can be caused by" and the following answer choices: 
- Pollution
 - nitric oxide
 - smoking
 - steroids
 - Pesticides
 - pollen
 - hormones
 - hydrogen peroxide

Now knowing that smoking causes direct damage to the lungs and with emphysema, there is permanent lung damage in the alveoli, choose the best answer.


 

   smoking      