Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
thanh cau » thanh chau, thanh mau, nhanh cau
hoc hieu » hoc thieu, hoc hien, doc hieu
cong tan » cong san, cong thanh, cong ty
cong tac » cong ty
cong va » dong va, luong va, cong san
cong ha » cong hoa, dong ha, cong san

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 quang - thanh ((cong va) or (cong ha)) thong ((cong tan) OR (cong tac)) thanh cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc hieu quang - thanh ((cong va) OR (cong ha)) thong ((cong tan) OR (cong tac)) thanh cau.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc hieu quang - thanh ((cong va) or (cong ha)) thong ((cong tan) OR (cong tac)) thanh cau".
• Adding a wildcard symbol may retrieve word variants: hoc hieu quang - thanh ((cong va) or (cong ha)) thong ((cong tan) OR (cong tac)) thanh cau*.