The correct answer is would have appreciated Key Points The subordinate clause of the sentence is in the past perfect tense (subject + had + third form verb). To maintain the uniformity of the sentence the main clause will have the structure as "would have + past participle". Hence, the main clause will take the verb phrase as:- "would have appreciated". The given sentence is a third conditional sentence. A third conditional sentence is used to imagine a different past that did not happen. Some Examples:- If I had been present, I should have enjoyed it a lot. If I had been present, I would have enjoyed it a lot. The correct sentence is- Father would have appreciated your efforts if you had informed him.