Fact 1: Biofuel is used to produce electricity by burning.

Fact 2: Ethanol is the most widely used biofuel today.

Given the two facts above, answer the question "what is used to produce electricity by burning?" with the following options: 
- air
 - heat
 - energy
 - cells
 - calcite
 - hydrogen
 - fire
 - ethanol


 

        ethanol 