Fact 1: Lung cancer is most often caused by exposure to tobacco smoke.

Fact 2: Many patients with lung cancer also have emphysema.

Given the two facts above, answer the question "Emphysema is often cause by exposure to:" with the following options: 
- high temperature
 - fog
 - Greenhouse gasses
 - rays or beams
 - hot steam
 - tobacco smoke
 - Pollution
 - incendiary people


 

      tobacco smoke   