Insert prepositions of time.

13. He was born ___ the fifth of June.
14. We have Art ____Monday and ___ Friday.
15. The first lesson ___Wednesday is Music.
16. I get up ____ 7 o’clock.
17. We have New Year____the first of January.
18. ____ end of the year we’ll have no exams.
19. I have studied English ___ four years.
20. We are going to meet ___ half past three.
21. The telephone rang ___ midnight.