The passive form of the sentence becomes This was done by whom?. For a more natural conversion, the word order can be inverted so that the interrogative, the words by whom?, come first. This question would be By whom was this done?, and means the same as the alternative.
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Answer:
The passive form of the sentence becomes This was done by whom?. For a more natural conversion, the word order can be inverted so that the interrogative, the words by whom?, come first. This question would be By whom was this done?, and means the same as the alternative.
Explanation: