The BBC also introduced Ceefax, the first teletext service, starting in 1974. This service allows BBC viewers to view textual information such as the latest news on their television. CEEFAX has not made a full transition to digital television, instead being replaced by the new interactive BBCi service.

Answer this question, if possible (if impossible, reply "unanswerable"): Ceefex replaced what interactive service?
unanswerable