Question

change voice - the municipality had sanctioned the construction of the theatre

Answer 1

the construction of the theatre had been sanctioned by the muncipality

Answer 2

Hi there !!
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Question :
The municipality had sanctioned the construction of the theatre

we're required to change in PASSIVE voice since the sentence is in active voice

Answer :
The construction of the theatre had been sanctioned by the municipality.

change in tens from simple past to past perfect ie, had to had been .