Perhaps you should try some spelling variations:
thanh dung » thanh duong, thanh tung, thanh hung
hieu lang » chieu sang, hieu quang, nhieu tang
cua thong » cua thuong, cua khong, suat thong
doc hieu » toc thieu, hoc thieu, hoc hien
cua tong » cua cong, cua dong, cua nong
van than » van thanh, van thang, van tuan
dan chan » dan gian, dan ca, van chat

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: doc hieu lang - thanh dung ((cua thong) OR (cua tong)) cong ((van than) OR (dan chan)) cap~.
• Adding a wildcard symbol may retrieve word variants: doc hieu lang - thanh dung ((cua thong) or (cua tong)) cong ((van than) or (dan chan)) cap*.