8. The door couldn't be opened of the room
9. The house have been cleaned up by Lan's parents before Tet holidays

8.The door of the room couldn't be opened
9.The house have to be cleaned up before Tet holidays by Lan's parents
10.A big cake were being made at 5 p.m yesterday
11.Tea is grown in Phu Tho 
12.Her car is being prepared now

Giải:

8. They couldn’t open the door of the room. =>The door of the room couldn't be opened

9. Lan’s parents have to clean up the house before Tet holidays. => The house has to be cleaned up by Lan's parents before Tet holiday

10. They were making a big cake at 5 p.m yesterday. => A big cake was being made at 5 p.m yesterday

11.  People grow tea in Phu Tho. => Tea was grown in Phu Tho

12. They are repairing her car now. => Her car is being repaired now