Answer:
B, but read the full explanation carefully. If you have an idea of your own, pick it.
Step-by-step explanation:
It's none of these. Later on we learn that they are talking about fortune and luck. Hamlet makes a very nasty comment about the nature of luck whom he sees as a changeable woman who takes money for her favors (his words not mine). Rosenkranz and Guildenstern are in the middle which leads Hamlet to make another off color observation.
Given that background, you could almost pick any one of the choices, since none of them are correct. I suppose if you take Guildenstern's initial couplet you could pick prosperity, but I wouldn't be surprised if the writer of this question didn't pick it. The quotation is taken out of context.
Whatever they are talking about is neither the top or the bottom. It is therefore in the middle. But before this speech, we learn that the two students are not doing well. Hamlet is trying to joke with them.