Fact 1: When electricity flows to a light bulb , the light bulb will turn on.

Fact 2: Coal-fired electric generation is a low cost source of electricity.

Given the two facts above, answer the question "A light bulb will turn on when something generated from what flows to it?" with the following options: 
- energy
 - gas
 - sun
 - SO2
 - copper
 - Coal
 - matter
 - wind


 

      Coal   