You are presented with the question "A light bulb will turn on when something generated from what flows to it?" and the following answer choices: 
- energy
 - gas
 - sun
 - SO2
 - copper
 - Coal
 - matter
 - wind

Now knowing that when electricity flows to a light bulb , the light bulb will turn on and coal-fired electric generation is a low cost source of electricity, choose the best answer.


 

      Coal   