Give the correct form of word air is a big problem in many cites in the world(pollute)?

1. Air ....pollution.... is a big problem in many cites in the world . ( pollute )

2. We should stop the enviroment ........pollution..... ( pollute)

3. We should use energy-saving bulbs. ( save)

4. The .........environmentalists........ are interested in protecting our enviroment . ( enviroment )

5. We brush our teeth ........2 times ..... daily ( twice )

6. Their ..........friendship....... lasts for 50 years . ( friend )

7.His ........flight......... is late because of the bad weather . ( fly )

8. He is very .....helpful........... . He often helps me wih difficult exercise ( help )

9.He is doing a very ......tiring......... work ( tired )

10. Nam is always ....busy............ ( business )

11. Tourists like the .........friendliness.......... of peope here ( friend )

12. Students need their ..........signature....... on their exam papers ( sign )

13. Lan's mother is ......careful....... ( care )

14.I'm sorry. I .....can't spell......your name ( spell0

15. she has some .......difficulties......... speaking English ( difficult )

16. The new ......product...... of that company is very good ( produce )

17. What is your ......suggestion....... about our weekend ( suggest )

18. Can you give me some .....suggestion............. ( suggest )

19. We should try to reduce ..........pollution... (pollute )

20. ..........pollution........... is a big problem in many big cities ( pollute )

21. The Earth climate is becoming .....warmer..... ( warm )

22. The storm is very .......destroyable....... ( destoy )