Fact 1: Boiling is when liquids are heated above their boiling point.

Fact 2: Boiling is the conversion of a liquid to a gas.

Given the two facts above, answer the question "What converts liquid to gas?" with the following options: 
- Stirring it
 - Fuel cells
 - circulatory systems
 - Cooling it down
 - Introducing oxygen
 - Heating it up
 - Evaporation
 - water vapor


 

      Heating it up   