Hello again, Ahmad,
All three sentences are possible, but (A) is possible only in British English. In American English, it is ungrammatical to say "go to hospital" or "go to university." We do, however, use "go to college."
In American English, (B) and (C) are both correct. I believe they are also possible for British speakers, whose English does not force them to talk in a way that American speakers find ungrammatical here.
ahmad posted:PS: I am taking it to be the case that there are more than one hospitals in the area, and that there is no prior reference to or any mention of any hospital etc.
Oddly enough, "more than one" takes singular agreement. You should say: "there is more than one hospital in the area." With there being no prior reference to a specific hospital, (C) means the same thing in American English that (A) means in British English. Compare: "Someone in this room has been to college."
Sentence (B) is rather unusual. It could be used in the context of a guessing game or riddle: "Someone in this room has been to a hospital today. Can you guess which hospital he went to?" The focus in (B) is on there being more than one possible hospital to which someone in this room went.