13. The climate will change unless we reduce the use of non-renewable energy.
-> If ........................................
14. Lock all the doors and noone can break into your house.
-> If ...........................................
15. Unless we continue hunting polar bears, they will become extinct in near future.
-> If ......................................... 
Cho dạng đúng của động từ trong ngoặc
1. If It (not rain) ………today, they ( go)…………camping.
2. Peter (play) ………soccer with his friends if he (have) …….free time.
3. If Jane (study) ………..harder, she (pass) …………….the entrance exams.
4. David (come and see) ……………….his girlfriend if he (not have to/work) ……..on a night shift.
5. This machine (break) ……..down if it (not use) ……..quite often.
6. Helen (come)…….. to class late if she (not run)…………….fast enough.
7. Giang’s parents (be)……..very happy if she (get) ……….good marks at school.
8. Thomas (visit) …….Ha Long Bay if he (earn) ……enough money.
9. If you (brush) ….your teeth regularly, you ( not have)……….a toothache.
10. If Carol (have) ….enough qualifications for the job she applied, she ( get) ……..it.