You are presented with the question "What causes lung tumors?" and the following answer choices: 
- oxidation reaction
 - cancer
 - Pollution
 - rays or beams
 - fossil fuels
 - diabetes
 - Pesticides
 - tobacco smoke

Now knowing that lung cancer is most often caused by exposure to tobacco smoke and lung cancer is a formation of tumors in the lung, choose the best answer.


 

        tobacco smoke 