Okay, first of all, your note is irrelevant in this case. Second, they never said anything like that in any of the gnostic gospels. Not only did I not think that they never said anything like that, but I just ran multiple searches through the KJV and several new versions, and I didn't find a single verse. I might have missed something, but yeah. Third, the answer is "it is he". While colloquial English has turned "it is he/she/I" into "it is him/her/me", that's technically wrong. "To be" is a nominative verb (that is, it's related to the subject, not the object), and since the subject pronouns are he/she/I, "it is he" is proper English. But it's also old English. English speakers have long since stopped caring about cases and declensions and crap like that; we're all about word order nowadays. So while you'd be hard-pressed to find someone ever say, "It is I" (in fact, it sounds pretentious and absurd to even say such a thing), that is the grammatically correct structure. Since we're dealing with the Bible here (and for the sake of the conversation, I'll be talking about the King James Version, from which much of modern English is derived), we're dealing with old English. Not only that, but we're also dealing with that whole self-referential thing that YHWH and its human incarnation like to do (e.g. "I am the LORD" and stuff like that). So, IF the disciples were to have ever said that in the four Gospels (again, they didn't to the best of my knowledge, and I know a pretty decent amount about those fables), they WOULD have said "It is he". In fact, the other three versions don't appear even once in the entirety of the KJV. tl;dr They never said any of those four things, but if we are to assume that they did say one of those four things, the answer is B.

I would say "It's me". Again, it sounds more natural to me. For example, "It's me who bought the gift." and not "It's I who bought the gift." Of course, time for the expert to explain the theory.

Thanks for the confirmation!

Your comments prompted me to open my grammar books which are covered with dust. Many suggest "He is taller than I." The Cambridge English Grammar in Use says "He is taller than me." and "He is taller than I am." are both ok. However, it is interesting to note there is a comment "not usually 'He is taller than I.' "

I think there is always an intended answer for every question. Sometimes we have to reverse engineer a bit, trying to guess what's in the question writer's mind. I would say both of them are acceptable. The former is more formal the latter is more casual. If I am asked by teacher or a grammar police, I would choose the former. Usually I would say "He is taller than me" simply because that's what I normally hear.