The answer is A. No person, powerful or weak, rich or poor, can escape the laws of God.
This theme runs through the entirety of Dante's Inferno. As we taken down through each circle of hell we are reminded how everyone no matter how they lived cannot escape the laws of God and that Gods word is all there is.
C and D are definitely themes in the book but not the central theme as such, hell is the platform for where the story takes place and each layer represents how a person's status in life reflects their punishment/fate in the afterlife. However the overarching theme is that God plans your fate.