The correct answer is: A. I was acknowledged by a great man to be a flatterer.
The sentence “A great man acknowledged me as a flatterer to him” is in the passive voice. The passive voice is used when the focus of the sentence is on the action, rather than the person or thing doing the action. In this case, the focus is on the fact that the great man acknowledged the speaker as a flatterer.
The active voice version of the sentence would be: “A great man acknowledged that I am a flatterer.”
The other options are incorrect because they do not accurately reflect the meaning of the original sentence. Option B, “I was acknowledged by a great man to have been a flatterer,” suggests that the speaker was once a flatterer but is no longer. Option C, “I am acknowledged as a flatterer by a great man,” suggests that the speaker is currently a flatterer. Option D, “I was acknowledged as a flatterer to a great man,” suggests that the speaker was once a flatterer to a great man but is no longer.