The Graph Shows the Temperature of a 1

The graph shows the temperature of a 1.0-g sample of material as heat is added to it. The material is initially a solid at 10°C. The pressure remains constant, and there is no chemical change. The heat of fusion of the material is

A) 10 cal/g.
B) 50 cal/g.
C) 30 cal/g.
D) 90 cal/g.
E) None of these is correct.