Student or Learner
This was one of China's 2005 university admission examination questions (for Shanddong Province):
It was some time ______ we realized the truth.
A. when B. until C. since D. before
The given answer was 'until', but I would think 'before' works as well. Am I right? My reason comes from:
Martin Hewings' ADVANCED GRAMMAR IN USE (2005 edition, Cambridge), unit 79:
We had to wait six weeks until/ before the parcel arrived.
It wasn't long before/until he was appointed Professor of Chemistry.
Both of these work ideally in the sentence you were given. 'Before' and 'until' have slightly different meanings, but overall their effect is identical.