The police officers _ to the theatre and every nook and corner was completely checked.

Explanation

The correct answer is B: 'were sent'. This choice accurately reflects the past tense passive voice. In this sentence, the police officers were the ones receiving the action of being sent, which is typical of a passive construction.Option A lacks the auxiliary verb needed for passive voice.Option C presents an active voice structure without the required auxiliary verb for passive construction.Option D uses the conditional perfect tense, which is inappropriate given the sentence's need for a simple past tense passive construction.