Distance, Force
Explanation:
1) Increasing the load will add to the friction on the bearings of the pulleys, thus reducing the efficiency of the system. The ideal mechanical advantage won't change since the ideal mechanical advantage ignores friction.
2) Increasing the number of pulleys will increase the ideal mechanical advantage, but because of friction it will decrease the efficiency. The more pulleys that are turning, the more friction there is, and the less efficient the system will be.
3) Work = force x distance, and what machines do is alter the amount of force you can apply while at the same time reducing the distance moved by the same factor. For instance, a jack multiplies the force you apply by a factor of 100, when you push down on the handle of the jack 100 cm, the car will only go up 1 cm. So the force x distance is the same 100 x force x 1/100 x distance.
