You are presented with the question "what produces carbon monoxide?" and the following answer choices: 
- h2o
 - burning coal
 - hydrogen
 - freezing
 - heating homes
 - chlorofluorocarbons
 - cigarettes
 - gasoline

Now knowing that carbon monoxide is a gas produced by furnaces and other devices that burn fuel and gas furnaces heat homes for up to 20 years, choose the best answer.


 

     heating homes    