Fact 1: The emission of sulfur dioxide causes acid rain.

Fact 2: It's sulfur dioxide (SO2).

Given the two facts above, answer the question "The emission of what causes acid rain?" with the following options: 
- H2O
 - smoke from food
 - Hydrogen
 - coal
 - SO2
 - oil
 - CFCs
 - Cars


 

     SO2    