Explanation

They had finished their homework by the time we arrived.

ہمارے پہنچنے تک وہ اپنا ہوم ورک ختم کر چکے تھے۔

The correct answer is "Had" because:

• The sentence uses the past perfect tense.
• The past perfect is used to show that one event happened before another event in the past.
• In this case, the homework was completed before "we arrived."