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

Fact 2: Tobacco is smoked in pipes or in cigarettes or bidis.

Given the two facts above, answer the question "What is lung cancer most often caused by?" with the following options: 
- the Moon
 - Pollution
 - sunlight
 - Chemical energy
 - fossil fuels
 - cigarettes
 - burning
 - marijuana smoke


 

      cigarettes   