Perhaps you should try some spelling variations:
thong cong » trong cong, tong cong, thong thong
hieu lang » chieu sang, hieu quang, nhieu tang
trinh cua » trinh luat, trinh quan, trinh luan
hoc hieu » hoc thieu, hoc hien, doc hieu
tinh cua » sinh cua, tinh chat, tranh cua
cong cac » cuong cac, cong tac, cong cau
chat van » chat ban, chat ran, chao van

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: hoc hieu lang - hanh ((trinh cua) OR (tinh cua)) thong cong cac ((chat van) OR (chat va))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc hieu lang - hanh ((trinh cua) OR (tinh cua)) thong cong cac ((chat van) or (chat va))~".
• Adding a wildcard symbol may retrieve word variants: hoc hieu lang - hanh ((trinh cua) OR (tinh cua)) thong cong cac ((chat van) or (chat va))*.