You are presented with the quiz "an incandescent light bulb converts electricity into light by sending electricity through what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "an incandescent light bulb converts electricity into light by sending electricity through a filament" and "fiber optics works by carrying light along hair-thin filaments of glass". 

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


 

        hair-thin fibers of glass   