In this English grammar question on Voice, the sentence "Who did this?" is given in Active Voice. Out of the options, choose the Passive Voice form that best expresses the same meaning.

Introduction / Context:
This grammar question checks your understanding of converting a question from Active Voice to Passive Voice. The original sentence is "Who did this?" You must select the passive form that is both grammatically correct and natural in standard English, especially with regard to word order and the correct use of "who" and "whom".

Given Data / Assumptions:

- Active Voice question: "Who did this?" - Subject in Active Voice: "Who". - Object in Active Voice: "this". - Verb: "did", which is the past tense of "do".

Concept / Approach:
To change an Active Voice question to Passive Voice, the object of the active sentence becomes the subject of the passive sentence, and the subject of the active sentence becomes the agent, usually introduced by "by". The verb "did" in the active sentence changes to "was done" in passive, since "this" is singular and the tense is simple past. In a formal question, "whom" is used after "by" because it functions as an object. The word order for a passive question is "By whom was this done?" which places the auxiliary before the subject, as is standard in English questions.

Step-by-Step Solution:

Verification / Alternative check:
To verify, convert the passive question back into the active form. From "By whom was this done?" move "this" to the object position and "whom" to the subject position. The structure becomes "Who did this?" which matches the original sentence exactly. The tense remains simple past, and the meaning is unchanged. This shows that the passive form has been correctly constructed.

Why Other Options Are Wrong:
Option A "This was done by who?" is grammatically less formal because "who" follows a preposition and should be in the objective form "whom" in standard usage, and it is not in question inversion format. Option B "By who this was done?" has incorrect word order for a question. Option C "By whom this was done?" again lacks proper inversion between auxiliary and subject, so it sounds like a statement fragment. Option E "Who was this done by?" is commonly used in informal speech, but in strict exam oriented grammar, "By whom was this done?" is preferred as the most correct passive interrogative form. Therefore option D is the best answer.

Common Pitfalls:
Students often struggle with the choice between "who" and "whom" in questions and also forget to invert the auxiliary verb and subject in passive interrogatives. Another frequent mistake is to keep the original subject order and simply add "by", which leads to ungrammatical sentences such as "This was done by who?". In exam conditions, always convert the object to the subject, use the correct passive form of the verb, and then ensure question word order by placing the auxiliary before the new subject.

Final Answer:
The correct Passive Voice form of "Who did this?" is "By whom was this done?", so the correct answer is "By whom was this done?".