The correct answer is B. Thus Fortune with a light / Turn of her wheel brings men from joy to sorrow.
The Monk's Tale is a bit different from all other plays in the Canterbury Tales - it is rather a collection of very short stories (17 of them) about various characters from literature and history who were played by Fortune. The moral of his story is that fate is fickle, and that you cannot control it. Your destiny decides what will happen to you, and there's nothing you can do about it.