You are presented with the question "What can release mercury into the atmosphere? " and the following answer choices: 
- smoking tobacco
 - hydrogen and oxygen
 - flow of electrons
 - cigarettes
 - chemical reaction
 - an engine
 - generating heat
 - one celled organisms

Now knowing that coal is used for generating heat by burning and coal releases mercury when it is burned, choose the best answer.


 

       generating heat  