Fill in the blank to complete the sentence

Word form
1. We have to try hard to save the (nature) ______ resources. 
2. There are about ten (apply) ______ for this position. 
3. He comes back school because of his teacher's (encourage) ______. 
4. English is the most (popularity) ______ language in the world. 
5. This work is very (differ) ______ from what you said to me. 
6. The Youth and Young is an (organize) ______ for teenagers in Viet Nam. 
7. He spends his free time doing (volunteer) ______ work in an orphanage. 
8. Mai speaks English (natural) ______ after two months living abroad. 
9. We are watching a film about how to protect the (environmental) ______.
10. You must ask your teacher (sign) ______ the application form. 
11. He has an ambition of (enroll) ______ for the Star-Up program. 
12. Can you tell me the (similar) ______ between two pictures?
13. Your (encourage) ______ words have helped me a lot in my study. 
14. Most people are impressed by your beautiful (collect) ______.