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

Fact 2: Tobacco smoke contains tar.

Given the two facts above, answer the question "Lung cancer is most often caused by exposure to" with the following options: 
- DDT
 - UV
 - methane
 - tar
 - CFCs
 - vapor
 - SO2
 - carbon dioxide


 

    tar     