Correct variant of construction
Not until the results were published ___ how serious the mistake had been.
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Верный ответ
- Adid the committee realise
Разбор
The sentence begins with the negative adverbial clause 'Not until the results were published'. When such a clause comes first, the main clause needs inversion: auxiliary verb + subject + main verb. The action 'realise' is in the past simple, so the auxiliary is 'did' and the main verb returns to its base form: 'did the committee realise'. 'the committee realised' has no inversion. 'had the committee realised' wrongly uses the past perfect, because the realisation came after the publication and is not earlier than it. 'the committee did realise' has an auxiliary but no inversion.