As Heat Is Slowly Added to a Glass of Ice

As heat is slowly added to a glass of ice water, the temperature remains at 0°C. Which of the following statements explains why the temperature of the mixture of ice and water remains constant as heat is added?

A) Heat is stored in the solid ice.
B) Heat is stored in the liquid water.
C) Heat is used to turn the solid ice into liquid water.
D) Heat is absorbed equally by the solid ice and the liquid water.