If I ______ you were coming, I might have stayed.

"If I ______ you were coming, I might have stayed."

The phrase "might have stayed" tells us this sentence is about an unreal past situation — something that didn't actually happen. This is a third conditional sentence, which follows the pattern:

If + had + past participle, ... might/would/could + have + past participle

So the blank needs "had known" (past perfect tense).

✅ Option 1: "had known" — fits the third conditional pattern perfectly. "If I had known you were coming, I might have stayed" means: "I didn't know you were coming, so I didn't stay — but if I had known, maybe I would have stayed!"

❌ Option 2: "know" — simple present tense; can't be mixed with "might have stayed," which is about the past.

❌ Option 3: "knew" — simple past tense; used in second conditional sentences about unreal present situations (e.g., "If I knew the answer, I would help you"), not past ones.

❌ Option 4: "have known" — present perfect tense; doesn't match the unreal past meaning of "might have stayed."

Hence, Option 1: "had known" is correct. ✅