The heating curve below shows the temperature change that occurs as a solid is heated. What is occurring at segment CD of the graph? (3 points)


A line graph showing the heating curve of a substance being heated from the solid phase all the way to the gas phase. From left to right across the x-axis, the different regions of the heating curve are labeled with variables A through F. First, there is an incline with a positive slope labeled AB, followed by a horizontal region labeled BC. Then there is another incline with a positive slope labeled CD, followed by another horizontal region labeled DE. The end of the heating curve shows another incline with a positive slope labeled EF.

boiling a liquid
melting a solid
heating a liquid
heating a solid