I think it would have be B because he want something that have to be done in a way that no one can do.
It refers to the person being addressed (not postitive)
The doorknocker is an important object, though. The doorknocker showed Scrooge Jacob Marley's face, in which led him through the events of the "night before Christmas" Without have seeing Jacob Marley's face he wouldn't have had any motivation.
