The best revision that changes the sentence to active voice is: 'Scientists reached a decision about when to begin the experiment.' This option clearly identifies the scientists as the ones making the decision, improving clarity. The other options maintain a passive structure and do not effectively highlight the action being performed by the subject.
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To revise the sentence from passive to active voice, use: "Scientists reached a decision about when to begin the experiment." This change emphasizes the doer and clarifies the meaning. The other options do not effectively achieve this transformation. ;