. . . . . he invited me, I would have attended his birthday party. A. Hardly had B. Had C. Had better D. If

The correct answer is: If.

The sentence “If he invited me, I would have attended his birthday party” is a conditional sentence. Conditional sentences are used to talk about things that are possible or probable. In this case, the speaker is saying that if the person had invited them, they would have attended the party.

The other options are not correct because they do not make sense in the context of the sentence.

• Hardly had: This phrase means “almost did not.” It would not make sense to say “I hardly had attended his birthday party.”
• Had: This is the simple past tense of the verb “to have.” It would not make sense to say “I had attended his birthday party.”
• Had better: This phrase means “should.” It would not make sense to say “I had better attended his birthday party.”

I hope this helps!