You are presented with the question "What is lung cancer most often caused by exposure to?" and the following answer choices: 
- Chemical energy
 - carbon dioxide
 - asbestos
 - sunlight
 - water
 - fossil fuels
 - cigarettes
 - hydrocarbons

Now knowing that lung cancer is most often caused by exposure to tobacco smoke and tobacco is most commonly smoked in cigarettes, choose the best answer.


 

       cigarettes  