1. They arrived very late because they had a flat tire. *
=> If 
2. I advise you not to say anything like that again. *
=> You’d 
3. You remember to post the letter, didn’t you? *
=> You didn’t 
4. “I’m sorry I gave you the wrong number”, said Paul to Susan. *
=> Paul apologized 
5. Please don’t smoke in the kitchen. *
=> I’d rather