Correct Answer:
B. wrote
The correct verb form to complete the question "Who __________ this letter?" is "wrote". This question requires the simple past tense because it refers to an action (writing a letter) that has already been completed at a definite point in the past. The question seeks to identify the person who performed this completed action.
- "Wrote" is the simple past tense form of the verb "to write." It correctly indicates that the action of writing the letter occurred and finished in the past.
- "Write" is the base form or present simple tense. It would be used for habitual actions or present facts (e.g., "Who writes letters regularly?"). It is incorrect here as the action is clearly past.
- "Written" is the past participle form. It is used with auxiliary verbs like "has," "have," or "had" to form perfect tenses (e.g., "Who has written this letter?") or in passive voice (e.g., "The letter was written by whom?"). Standing alone, it is grammatically incomplete.
- "Writing" is the present participle form. It is used with forms of "to be" to create continuous tenses (e.g., "Who is writing this letter now?") or as a gerund. It does not fit the context of a completed past action.
Therefore, the grammatically correct question is: "Who wrote this letter?"