Boiling is when liquids are heated above their boiling point.
Boiling is the conversion of a liquid to a gas.
Heating liquids above a certain temperature converts to gas.
What converts liquid to gas?

[1] Stirring it
[2] Fuel cells
[3] circulatory systems
[4] Cooling it down
[5] Introducing oxygen
[6] Heating it up
[7] Evaporation
[8] water vapor