You are presented with the quiz "What happens when a fuel burns incompletely?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "carbon monoxide is a gas produced by furnaces and other devices that burn fuel" and "any fuel that is incompletely burned produces carbon monoxide, a colorless, odorless gas". 

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


 

    Carbon monoxide is created       