We're drifting off topic but, for the record, this is what the B737 manual says:
'..when external position updating is not available navigation accuracy may be less than required. Flight crews should closely monitor FMC navigation, especially when approaching the destination. The accuracy of the FMC navigation should be determined during the descent phase by using radio navaids and radar information if available.'
On re-reading the paragraph I think Oxford Blue's objection still stands. I read it only one way but the manual could be implying bad fixing either at TOD or on final approach. Have you queried this with the CAA?
To be fair to the CAA they do operate a filter system where questions queried by either the candidates or the CGIs are reviewed by FCL after the exams. In April they credited 19 questions spread over 14 papers, in March they took out a similar number. Those taking the exams this week will find several 'question deleted' marks in the papers where the offending questions have been removed.
Send Clowns: The old CAA version of your question had an answer 'all of the above'. I wonder why it was changed?
Back on topic, I heard the other day that version 3 of the Central Question Bank (we're now at version 6 or 7) was for sale on the web for $10,000 a pop. I can't find it!