Traditional iron ingot complete collection

Iron is a crystal, and its temperature remains constant during melting.

A, the temperature has a downward trend, and the temperature changes constantly during the solidification process, which is an amorphous solidification image and does not meet the meaning of the question;

B, the temperature tends to rise, which is a melting image and does not meet the meaning of the question;

C, the temperature tends to rise in the whole process, which is a melting image and does not meet the meaning of the question;

D, the temperature has a downward trend during the whole process, and the temperature remains unchanged during the solidification process, so it is the solidification image of the crystal, which conforms to the meaning of the question.

So choose D.