21. The improvements of the public transport system will encourage more people to use it.

→ If____________________________________________________________

22. Remember to turn off the fan before leaving the room.

→ Don't ________________________________________________________

23. That man is very intelligent.

→ What ________________________________________________________ 

24. I intended to come over to pick you up.

→ I was ________________________________________________________

25. My sister's hair is long and black.

→ My sister has __________________________________________________

26. Phillip had gone out before they arrived.

→ After  ____________________________________________________________

27. I had lunch then I watched an interesting film.

→ Before ___________________________________________________________

28. There was a power cut before they got out of the room.

→ When ____________________________________________________________

29. After the manager had informed us clearly about the job, we started our work.

→ By the time ________________________________________________________

30. Henry arrived at the meeting at 7 o’clock. I arrived at 6:45. (soon)

--> I __________________________________________________________