You are presented with the quiz "What are the affects of burning fuel on human health?" 

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 "carbon Monoxide Carbon monoxide is a health hazard". 

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


 

    They are a hazard.       