Perhaps you should try some spelling variations:
thanh trung » thanh tung
nhung cong » dung cong, thong cong, hang cong
trung cua » truong cua, trung tuan, trung cap
cua nhung » va nhung
hieu cac » hieu va, hieu van, vien cac
hieu luc » hieu luat, hieu qua
dan toan » van toan, dan than, manh toan
dan chan » dan gian, dan ca, van chat

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 cac) OR (hieu luc)) - thanh trung cua nhung cong ((dan toan) or (dan chan)) cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((hieu cac) OR (hieu luc)) - thanh trung cua nhung cong ((dan toan) OR (dan chan)) cau.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((hieu cac) OR (hieu luc)) - thanh trung cua nhung cong ((dan toan) or (dan chan)) cau".
• Adding a wildcard symbol may retrieve word variants: hoc ((hieu cac) OR (hieu luc)) - thanh trung cua nhung cong ((dan toan) or (dan chan)) cau*.