You are presented with the quiz "A light bulb will turn on when something generated from what flows to it?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says 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". 

So, what's the best answer to the question?


 

      Coal     