The diagram shows a heating curve for a substance. A graph titled heating curve of Substance It shows heat added in joules on the x-axis, and temperature in degrees celsius on the y-axis on a scale of 0 to 100. The graph has a diagonal line from negative 5 degrees up to zero degrees labeled U. A horizontal line segment at zero degrees labeled V. A diagonal line segment from zero degrees up to 120 degrees labeled W. A horizontal line segment at 120 degrees labeled X and then another diagonal segment labeled Y.

Which segment shows the substance changing from a gas to a liquid?