You are presented with the question "When is coal burning _ is given off" and the following answer choices: 
- CO 2
 - energy
 - vaporization
 - SO2
 - pollution
 - oxygen
 - carbon
 - smoke

Now knowing that coal is used for generating heat by burning and cO 2 and SO 2 are both given off when coal is burned to provide heat or to generate electricity, choose the best answer.


 

 CO 2        