Perhaps you should try some spelling variations:
thong cong » trong cong, tong cong, thong thong
hieu lang » chieu sang, hieu quang, nhieu tang
hanh sinh » hanh tinh, hanh dinh, hinh sinh
dang cong » dung cong
trinh han » trinh quan
doc hieu » toc thieu, hoc thieu, hoc hien
sinh cua » manh cua, dinh cuu, sinh va
han dau » hang dau, phan dau, van dau

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 - hanh sinh cua ((thong cong) OR (dang cong)) trinh han dau~.
• Adding a wildcard symbol may retrieve word variants: doc hieu lang - hanh sinh cua ((thong cong) or (dang cong)) trinh han dau*.