Perhaps you should try some spelling variations:
duong quag » duong quang, duong quan, luong quang
quang quan » quang tuan, quang uan, quan quan
hieu soat » hieu suat, hieu hoat, hieu luat
kiem soat » kiem toan
van hieu » cao hieu
quan van » luan van, quan va, quan luan
van kiem » va kiem, van kien, van hien

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: (( tinh ((duong qua) OR (duong quag)) van hieu soat ) OR ( tinh quang quan van kiem soat ))~.
• Adding a wildcard symbol may retrieve word variants: (( tinh ((duong qua) or (duong quag)) van hieu soat ) or ( tinh quang quan van kiem soat ))*.