Perhaps you should try some spelling variations:
quan trong » gian trong
cong thanh » dong thanh, cong trinh, truong thanh
hieu lang » chieu sang, hieu quang, nhieu tang
hanh tang » hanh trang, anh tang, hanh tung
hanh mang » nhanh mang, hanh trang, nhanh lang
cong tan » cong tac, cong san, cong ty
toan tap » toan ban
he hieu » he nhieu, he dieu, de hieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: he hieu lang - ((hanh tang) or (hanh mang)) quan trong ((cong tan) OR (cong thanh)) toan tap~.
• If you are trying to use Boolean operators, they must be ALL CAPS: he hieu lang - ((hanh tang) OR (hanh mang)) quan trong ((cong tan) OR (cong thanh)) toan tap.
• The words AND, OR and NOT may confuse the search; try adding quotes: "he hieu lang - ((hanh tang) or (hanh mang)) quan trong ((cong tan) OR (cong thanh)) toan tap".
• Adding a wildcard symbol may retrieve word variants: he hieu lang - ((hanh tang) or (hanh mang)) quan trong ((cong tan) OR (cong thanh)) toan tap*.