`1.`If you don't study harder, you‘ll fail the next exam.

`->` Unless you study harder, you‘ll fail the next exam.

`2. `If he doesn't practice writing every day, he can't improve his writing skill.

`->` Unless he practices writing every day, he can't improve his writing skill

`3.`Unless this man is a driver, he can’t help you move by car. 

`->` If this man is not a driver, he can’t help you move by car.

`4. `Unless you go out more often, you might fall ill.

`->` If you go out more often, you might fall ill.

`5.` If you don’t return this book to the library today, you’ll have to pay a fine.

`->` Unless you return this book to the library today, you’ll have to pay a fine.

`6.` Unless he cleaned up the car now, his boss could ask him to do this.

`->` If he didn’t clean up the car now, his boss could ask him to do this.

`7.` Unless they were absent now, they would meet the headmaster.

`->` If they were not absent now, they would meet the headmaster.

`8.` If I didn’t know the number, I would not ring her up.

`->` Unless I knew the number, I wouldn't ring her up.

`9`. If my sister didn’t have a terrible headache she wouldn’t be absent from her class.

`->` Unless my sister had a terrible headache, she wouldn’t be absent from her class.

`10.` If Peter didn’t study hard, he could not get good marks.

`->` Unless Peter studied hard, he couldn't get good marks.

- If + S + V(s/es) + ...,S+ will/can/... (+not) + V(o) + ...

- If + S + V2/V-ed+ ...,S + would/could/... (+not) + V(o) + ....

- If + S + had + VpII + ...S + would/could/... + have + VpII + ...

- Unless = If...not = Trừ khi

1.If you don't study harder, you ‘ll fail thenext exam.

=> 1. Unless you study harder,you ‘ll fail the next exam.

2. If he doesn't practice writing every day, he can't improve his writing skill.

=>2. Unless he practices writing every day, he can't improve his writing skill

3.Unless this man is a driver, he can’t help you move by car. 

=> 3. If this man is not a driver, he can’t help you move by car.

4. Unless you go out more often, you might fall ill.

=>4. If you go out more often, you might fall ill.

5. If you don’t return this book to the library today, you’ll have to pay a fine.

=>5. Unless you return this book to the library today, you’ll have to pay a fine.

6. Unless he cleaned up the car now, his boss could ask him to do this.

=>6. If he didn’t clean up the car now, his boss could ask him to do this.

7. Unless they were absent now, they would meet the headmaster.

=> If they were not absent now, they would meet the head master

8. If I didn’t know the number, I would not ring her up.

=>Unless I knew the number, I would not ring her up.

9. If my sister didn’t have a terrible headache she wouldn’t be absent from her class.

=> Unless my sister had a terrible headache she wouldn’t be absent from her class.

10. If Peter didn’t study hard, he could not get good marks.

=> Unless Peter studied hard, he could not get good marks.

Unless = If….not (Nếu ………không, trừ phi)

Chú ý: Khi đổi một câu điều kiện với từ nối IF sang UNLESS, lưu ý không được đổi sang thể phủ định khi dùng UNLESS (unless….not) mà phải đổi mệnh đề chính sang thể ngược lại