Answer: D) the difference in the positioning of the effort (force), load, and fulcrum
Explanation: Lever is the simple machine that has ability to rotate on its own in accordance with point.It is based on the working that is carried out by the different position load,force and fulcrum factors.These factors decide the movement and location the lever tends to move and work.
Other options are incorrect because person's muscle does not manage the lever working.weight and direction of the load is not the controlling factor rather it's position matters for the lever .Thus the correct option is option(D)