IV-Rewrite. 
20. If you don’t return this book to the library today, you’ll have to pay a fine.
=> Unless ………………………………………………………………..
21. Unless he washed up the car now, his boss could ask him to do this.
=> If …………………………………………………………………
22. Unless they were lazy now, they would meet the headmaster.
=> If …………………………………………………………………
23. If I didn’t have the number, I would not ring her up.
=> Unless …………………………………………………………………
24. If my sister didn’t get a terrible headache she wouldn’t be absent from her class.
=> Unless …………………………………………………………………  
Giải hết giúp e vs ạ