Perhaps you should try some spelling variations:
hieu lang » chieu sang, hieu quang, nhieu tang
dang cong » dung cong
hoc hieu » hoc thieu, hoc hien, doc hieu
van dang » van dong, van dung, van nang
cong tac » cong ty
tac than » tac thanh, tam than, tac nhan
than cao » toan cao, thai cao, than cap

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc hieu lang - ((thanh tung) or (thanh cong)) van dang cong tac than cao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc hieu lang - ((thanh tung) OR (thanh cong)) van dang cong tac than cao.
• Adding a wildcard symbol may retrieve word variants: hoc hieu lang - ((thanh tung) or (thanh cong)) van dang cong tac than cao*.