Fact 1: Burning fossil fuels increases the carbon in the atmosphere.

Fact 2: Fossil fuels are not sustainable fuels.

Given the two facts above, answer the question "What sort of fuel burning puts carbon into the atmosphere?" with the following options: 
- Greenhouse gases
 - Organic compounds
 - vehicles
 - Pollution
 - non-sustainable
 - chlorofluorocarbons
 - Conifers
 - an engine


 

     non-sustainable    