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

Fact 2: Polluted rain is called acid rain .

Given the two facts above, answer the question "What causes pollution in rain?" with the following options: 
- sulfur dioxide
 - carbon dioxide
 - nitrogen
 - contamination
 - smog
 - hydrogen
 - fossil fuels
 - flooding


 

 sulfur dioxide        