In the diagram, which letter represents the transition from gas to liquid?

B

C

D

E

A graph in five sections, labeled A through E. Horizontal axis has no scale and is labeled Amount of heat added. Vertical axis is labeled Temperature, in degrees Celsius, and extends from negative 100 to 200 with an interval of 50. Section A of the graph is a line segment with positive slope that begins at negative 100 degrees and ends at 0 degrees. Section B is a horizontal line segment that begins where segment A ends, at 0 degrees. Section C of the graph is a line segment with positive slope that begins where segment B ends, at 0 degrees, and ends at 100 degrees. Section D is a horizontal line segment that begins where segment C ends, at 100 degrees. Section E of the graph is a line segment with positive slope that begins where segment D ends, at 100 degrees, and ends at 200 degrees