Perhaps you should try some spelling variations:
cac khoi » cac thoi, cac khoan, cach thoi
khoi may » khoi bay, khoi xay, khoa ma
su sach » so sach, vu sach
hieu ve » hieu va, hieu van
tinh vi » trinh vi, tinh voi, tinh va
ly van » le van, ly va, lo van
ve cac » va cac, vien cac
vi cua » vai cua, di cua
cua te » cua tu

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ((ly van) or (ly von)) xa hoi. hieu ve cac khoi may tinh vi cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((ly van) OR (ly von)) xa hoi. hieu ve cac khoi may tinh vi cua te.
• Adding a wildcard symbol may retrieve word variants: su sach ((ly van) or (ly von)) xa hoi. hieu ve cac khoi may tinh vi cua te*.