Change the sentence “let it be done at once” into active voice.

The sentence 'Let it be done at once' is a passive imperative with the pattern 'Let + object + be + past participle'. To change it to active voice, find the doer. In an imperative the doer is the implied 'you', so we drop 'Let it be done' and write 'Do it' directly. The sense stays the same: act on it immediately.

• A is wrong because 'happen' is intransitive. It shifts the meaning from someone acting to an event occurring.
• B is wrong because 'atleast once' means 'at least one time', a different phrase from 'at once', which means immediately.
• C is wrong for the same reason as A: 'occur' is intransitive and turns an action into an event.
• D is correct: 'Do it at once' keeps the imperative mood and the urgency.

Core concept: voice conversion in imperatives, where 'Let it be done' becomes 'Do it'. In Mains, this precision matters for drafting official communication and clear English essays.

Trap: aspirants see 'let' and reach for the 'Let + object + verb' pattern, picking A or C, or they miss that 'atleast once' in B is a different phrase.