Welcome David21,
I hope I'm understanding your question. First I will assume you are playing no limit, because if it is a limit game Player B might not have an option to raise.
If only Players A & B are in the hand (heads up), Player B must call the all-in. If multiple players, if Player B said "raise," which you did not indicate...he might be held to a minimum raise. He will not be allowed to retract his call no matter what Player's C or D do.