You are presented with the question "Carbon monoxide, a product of furnaces and engines, is a:" and the following answer choices: 
- acid
 - CO2
 - kill
 - harm
 - gas
 - form
 - CO 2
 - HPV

Now knowing that carbon monoxide is a gas produced by furnaces and other devices that burn fuel and fuel is burned inside the engine, choose the best answer.


 

     gas    