How often is there a World Expo?

Related questions

1. When and where is the next World Expo?
2. How long will the World Expo last?
3. Why is Masdar City being built?
4. What is the theme of Dubai Expo 2020?
5. How will Dubai Expo 2020 make the world a better place?
6. How often is World Expo?
7. Is there still a world fair?
8. Do worlds fairs still exist?
9. What is the purpose of an Expo?
10. Where is the next Expo being held?

Tags

1. #expos
2. #years
3. #limited
4. #registered
5. #calls
6. #which
7. #recognized
8. #world
9. #often
10. #duration
11. #registers
12. #recognizes
13. #occur
14. #above
15. #every
16. #between
17. #agency
18. #fairs