A water pumping station found that its electricity consumption (unit: kilowatt-hours) is directly proportional to the cube of the pump motor speed (unit: rpm). Based on this, which of the following five graphs best describes the relationship between the electricity consumption $y$ (kilowatt-hours) and the pump motor speed $X$ (rpm) of this water pumping station?
(1) [Graph 1]
(2) [Graph 2]
(3) [Graph 3]
(4) [Graph 4]
(5) [Graph 5]