Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu qua, diep quang
hieu quan » hieu qua, lieu quan, thien quan
huong cua » dung cua
cong cong » cong dong, trong cong, dung cong
cong tan » cong tac, cong san, cong thanh
tan toan » tan tran, tap toan, van toan
toan cao » toan ban, toan tap

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

• If you are trying to use Boolean operators, they must be ALL CAPS: doi ((hieu quang) OR (hieu quan)) - hanh ((huong cua) OR (nang cao)) cong cong tan toan cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doi ((hieu quang) OR (hieu quan)) - hanh ((huong cua) or (nang cao)) cong cong tan toan cao~".
• Adding a wildcard symbol may retrieve word variants: doi ((hieu quang) OR (hieu quan)) - hanh ((huong cua) or (nang cao)) cong cong tan toan cao*.