Convert the sentence from passive voice to active voice: The machinery was known to have been operated manually during the testing phase.

Manual operators were known to test the machinery.
Someone was known to operate the machinery manually during testing.
It was known that the machinery had been manually tested.
It was known that someone had manually operated the machinery during the testing phase.

Correct answer: It was known that someone had manually operated the machinery during the testing phase.

Solution

The phrase 'was known to have been operated' indicates a passive perfect infinitive. To convert it into a more active structure, we express the action as something 'someone had manually operated' during the testing phase.

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