Improve the sentence by selecting the appropriate tense of the highlighted word.
By the time you arrive, we finishes dinner.

Correct option is D

The correct substitution of the highlighted words is (d) will have finished.
Explanation: With the time-clause “By the time you arrive” (simple present for a future reference point), the main clause should show an action completed before that future moment. English uses the future perfect (“will have + V3”) to mark prior completion relative to a future time. Also, subject–verb agreement requires we finish, not we finishes. Thus, “By the time you arrive, we will have finished dinner.”
Grammatical rule used: By the time + simple present (future reference) → main clause in future perfect (will have + past participle).
Example: By the time the movie starts, I will have found my seat.
Information booster: If the reference point is in the past, we use past perfect in the main clause: By the time she arrived, we had finished dinner.