Rewrite the sentences

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 …………………………………………………………………