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def solution(stationsA, stationsB, stationsC, origin, destination):
    zoneA = set(stationsA)
    zoneB = set(stationsB)
    zoneC = set(stationsC)

    if origin in zoneA and destination in zoneC or origin in zoneC and destination in zoneA:
        return "ABC"
    elif origin in zoneA and destination in zoneB or origin in zoneB and destination in zoneA:
        return "AB"
    elif origin in zoneB and destination in zoneC or origin in zoneC and destination in zoneB:
        return "BC"
    else:
        return ""