You are presented with the quiz "What is NOT a byproduct of using a gasoline engine?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "using a gasoline engine requires burning gasoline" and "for every one gallon of gasoline an engine burns, one gallon of water is produced as a by-product". 

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


 

        uranium   