Hm. Well I'm going to guess that he doesn't have the mens rea for felony murder. But he did intend to shoot Belle, so I'm ruling out D too. So I guess the question is how serious was the arm shooting. Pretty serious, obviously, and the question asks for the most serious crime, so I'm going to say B. Alternatively, D. Then C. Then A.
ETA: Now that I think about it, I've never heard of B, so I bet it's D, since that might involve not having the mens rea for murder, yet negligently/recklessly inflicting bodily injury that could lead to death. So I change my mind and say D.