Boiling means change from a liquid into a gas by adding heat energy.
Boiling water produces steam.
When enough heat energy is added to water, it becomes steam.
What causes water to become steam?

(A) Condensation
(B) movement of tectonic plates
(C) Increasing pressure
(D) an engine
(E) evaporation
(F) heating liquids
(G) Reducing temperature
(H) Adding heat energy