You are presented with the question "Emphysema is often cause by exposure to:" and the following answer choices: 
- high temperature
 - fog
 - Greenhouse gasses
 - rays or beams
 - hot steam
 - tobacco smoke
 - Pollution
 - incendiary people

Now knowing that lung cancer is most often caused by exposure to tobacco smoke and many patients with lung cancer also have emphysema, choose the best answer.


 

      tobacco smoke   