Answer:
B-C and D-E
Explanation:
In segment B-C the substance is changing from a solid to a liquid (melting). There is no change in temperature because the heat is being used to separate the particles from the solid and move them into the liquid phase.
In segment D-E the substance is changing from a liquid to a gas (boiling). There is no change in temperature because the heat is being used to separate the particles from the liquid and move them into the gas phase.
C-D is wrong. The liquid is being heated from its melting point to its boiling point.
D-C is wrong. The liquid is being cooled from its boiling point to its melting point.
E-F is wrong. It represents heating of the gas.
