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

Fact 2: Natural gas is the cleanest of the fossil fuels.

Given the two facts above, answer the question "Burning which of these increases carbon in the atmosphere?" with the following options: 
- wind energy
 - natural gas
 - green manures
 - Greenhouse gases
 - solar energy
 - Conifers
 - engines
 - oxygen


 

  natural gas       