Correct option is A
The correct expression in active voice is (a) "The researchers did not analyse the data carefully."
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Active Voice- Active voice is a grammatical structure in which the subject of the sentence performs the action expressed by the verb.
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Passive Voice- Passive voice refers to a grammatical construction where the subject of a sentence undergoes an action rather than performing it. In passive voice sentences, the emphasis is on the recipient or object of the action.
Conversion rule:
Past indefinite
Subject + did not V1 + object. -> <- Object + auxiliary verb (was, were) not + past participle + by + subject.