The answer is (d): other, as seen in an mpeg video by clicking your mouse on the photograph below.
This is a "gag" pulley system called the "Fool's Tackle" in physics literature. It only seems to function because the rope is pinned to the "free" pulley and there is enough tension in the loop to support the weight of that pulley. This pulley system is included as a Question of the Week to see how many of you look at it and have an intuitive feeling that something is wrong. If you did not, don't feel bad; about 90% of physics professors initially fall for this one if they have not seen it before.
There are a whole series of pulley systems of this type that either do nothing or are impossible to construct, but look good on paper. This trick is apparently sometimes used as an initiation gag for new sailors: the captain draws one and tells the novice to go down to the hold and make it, but when the system is released it immediately falls to the floor!!
Using the technique taught in elementary physics classes to analyze pulley systems suggests this unusual result; lamentably, very few people analyze the problem in this way. Consider the following: When you apply a small force dF on the free end of the rope, the force should be transmitted uniformly throughout the rope. There would be a force of dF pulling up on the free pulley, but a force of 2dF pulling down! Does this mean that the pulley would have to move down, leading one to conclude that perhaps there is something wrong here, or perhaps that it is unstable in the first place.
