Section A and ab are the melting process of naphthalene, and the corresponding temperature is 80℃, so the melting point of naphthalene is 80℃, which is correct.

B, ab section in the figure shows the melting process of the crystal. In this process, the temperature remains the same, but nai still absorbs heat. This statement is wrong.

C, in the figure, the ab section is the melting process of the crystal, that is, the crystal is melting, so it shows that nylon is in a state of solid-liquid coexistence in the ab section and naphthalene is in a state of solid-liquid coexistence in the ab section, which is correct.

D. Naphthalene began to melt in the 3rd minute and ended in the 7th minute, so the melting process of naphthalene lasted for 4 minutes, which is correct.

So choose ACD. ..