Correct Answer:
C. had written
This sentence describes two past actions: "writing the letter" and "he arrived." To correctly show that one action happened before another in the past, we use specific tenses. The word "before" is a crucial indicator of this sequence.
- The correct answer is C: "had written." This is the Past Perfect tense, formed by "had" + the past participle of the verb. The Past Perfect is used for an action that was completed before another action in the past. Here, "She had written the letter" indicates that the letter was finished prior to "he arrived" (Simple Past).
- A: "wrote" is the Simple Past tense. While it describes a past action, using it for both actions ("She wrote the letter before he arrived") would imply a simple sequence but wouldn't emphasize the completion of the first action *prior* to the second as clearly as the Past Perfect does.
- B: "writes" is the Simple Present tense, used for habitual actions or general truths, not for a sequence of past events.
- D: "writing" is a present participle. It cannot stand alone as the main verb in this sentence without an auxiliary verb (e.g., "was writing" for Past Continuous), and even then, Past Continuous would imply an ongoing action, not a completed one before another event.
Thus, "had written" correctly establishes the chronological order of the two past events.