A substance X was heated at constant pressure and the temperature observed at various times of heating was plotted as given below

Which of the following is or are correct?

I. Melting point of X is $$-5^\circ\text{C}$$. 

II. Solid and liquid forms of X coexist in the region b. 

III. Boiling point of X is $$55^\circ\text{C}$$.

IV. Solid and liquid forms of X coexist in the region d

A

I and IV

B

II and III

C

III only

D

I, II and III