24. He decided to leave the country for ______(各种) reasons.　

23. The children come from a _____(多种) of different backgrounds.　

22. The ____(大多数)of students find it hard to live on the amount of money they get.

21. It ______(需要)ten percent of all cars sold in the state to be pollution-free.

20. ______(生物学) is the science and study of living things.

19. Mr. Liu’s good English and teaching _______ (经验)do count.

18. The teacher should have the ability to give clear ________(解释).　

17. All the necessary details and _______(可能性) are included.

16. In countries where it’s difficult to get an education, people ____(珍惜)it more when they do get it.　

15. Students in the school need several ______(图书馆) for knowledge.