The diagram shows an investigation in a science classroom.
Students pull the same mass up an inclined plane propped up on five blocks and then six, seven, and eight blocks. Each time, they use a spring scale to measure the force needed to pull the mass up the inclined plane. This investigation can show how which of the following affects the force needed to move an object up an inclined plane?
A The mass of the object
B The surface area of the object
C The height of the inclined plane
D The length of the inclined plane