You are presented with the question "what is added to propane to change it through the boiling process" and the following answer choices: 
- vapors
 - energy
 - pH
 - heat
 - fats
 - SO2
 - fusion
 - oxygen

Now knowing that boiling means change from a liquid into a gas by adding heat energy and propane can be either a liquid or a gas, choose the best answer.


 

    heat     