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

Fact 2: Lung cancer is a formation of tumors in the lung.

Given the two facts above, answer the question "What causes lung tumors?" with the following options: 
- oxidation reaction
 - cancer
 - Pollution
 - rays or beams
 - fossil fuels
 - diabetes
 - Pesticides
 - tobacco smoke


 

        tobacco smoke 