The correct answer is:
A. Because the supplied heat is used to overcome the force of attraction between the molecules.
During the process of melting, heat energy (known as latent heat) is absorbed by the solid as it transitions into a liquid. This energy is used to break the bonds between the molecules in the solid, allowing them to move more freely, rather than increasing the temperature of the substance. Therefore, the temperature remains constant during the melting process even though heat is being added.