You are presented with the question "What sort of fuel burning puts carbon into the atmosphere?" and the following answer choices: 
- Greenhouse gases
 - Organic compounds
 - vehicles
 - Pollution
 - non-sustainable
 - chlorofluorocarbons
 - Conifers
 - an engine

Now knowing that burning fossil fuels increases the carbon in the atmosphere and fossil fuels are not sustainable fuels, choose the best answer.


 

     non-sustainable    