Explanation

This sentence belongs to Present Continuous Tense.

Active voice formula: Subject + am/is/are + present participle (verb+ing) + the rest of the sentence

Passive voice formula: Object + is/am/are + being + third form of verb + by + subject

Active voice: The students are decorating the stage for the annual day celebrations

Passive voice: The stage is being decorated by the students for the annual day celebrations

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