Giải 

21. Only when your identity has been checked will you be admitted.

22. Hardly had the play started when there was a power failure.

23. Rarely has the Prime Minister made so inept a speech.

24. Scarcely had we arrived home when the police called.

25. On no account are press photographers allowed to take photographs backstage.

26. Never before has so much money been spent to so little purpose. 

27. Barely had the trial proceedings begun when the judge was taken ill.

28. Seldom does she miss a lecture.

29. No sooner had we come home than it started to rain.

30. Hardly had we turned on the TV, the electricity went out.

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21. Only when your identity has been checked will you be admitted.

22. Hardly had the play started when there was a power failure.

23. Rarely has the Prime Minister made so inept a speech.

24. Scarcely had we arrived home when the police called.

25. On no account are press photographers allowed to take photographs backstage.

26. Never before has so much money been spent to so little purpose. 

27. Barely had the trial proceedings begun when the judge was taken ill.

28. Seldom does she miss a lecture.

29. No sooner had we come home than it started to rain.

30. Hardly had we turned on the TV, the electricity went out.