Fact 1: Riding a bike does not cause pollution.

Fact 2: City employees use bicycles on the job to save energy and reduce air pollution.

Given the two facts above, answer the question "Riding a bike reduces what?" with the following options: 
- energy usage
 - Greenhouse gasses
 - acid rain
 - harmful substances
 - Greenhouse gases
 - temperature
 - prolactin release
 - storms


 

 energy usage        