Topic: Sequence of Tense,

Best Answer Explained in Below-:

In the sentence "Mary--her homework when we arrived. So we all went out for the evening," the context indicates that Mary's completion of her homework occurred before the time we arrived. Therefore, we need an appropriate verb tense that conveys this sequence of events.

The option "C) had finished" uses the past perfect tense, which is specifically designed to describe an action that was completed before another action in the past. Here, "her homework" was finished before "we arrived." This simultaneous relationship necessitates using the past perfect tense to clearly indicate that Mary completed her homework prior to our arrival.

The other options do not fit this context effectively.

- "A) has finished" uses the present perfect tense, which is inappropriate here as it suggests relevance to the present, rather than a sequence in the past.
- "B) is finishing" uses the present continuous tense, implying that the action is still ongoing, contradicting the idea that the homework was completed.
- "D) was finished" suggests that someone or something else completed the homework without emphasizing Mary as the subject performing the action.

In summary, "had finished" correctly establishes the temporal relationship between the actions, making it the most suitable choice.