A. Because the source would have a wide spectrum of information and would lead you to other sources for more specific information.
A similarity they both share is the fact that the death of multiple man is heavily present in both stories however their locations and background are completely different.
Hope this helps :)
Ok then......................................
What makes them similar is that that both Charrington and O'Brien seem to be on Winston's side, i.e. against the Party. Another similarity is that they both end up betraying him, essentially they deceived him by hiding their true intentions from him. Charrington uses a literal disguise, while O'Brien was just pretending to be something he is not.
