Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
hieu quan » hieu qua, lieu quan, thien quan
hanh hang » thanh hang, hang hang, hanh han
hoc hieu » hoc thieu, hoc hien, doc hieu
cong dan » cong san, cong tan, huong dan
toan tai » toan tap, toan cao, von tai
toan ban » van ban

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 quan - hanh hang va nhung cong dan ((((toan tai) OR (doanh tai))) OR (toan ban))~.
• Adding a wildcard symbol may retrieve word variants: hoc hieu quan - hanh hang va nhung cong dan ((((toan tai) or (doanh tai))) or (toan ban))*.