What is heat vaporization?

A)it is the heat required to change a substance’s temp by 1degreeC.
B)it is the heat required to change a gram of substance from a solid to a liquid.
C)it is the heat required to change a substance from a solid directly to a gas.
D)It is the heat required to change a gram of substance from a liquid to a gas.
E)It is the heat required to separate one substance into two substances.