Perhaps you should try some spelling variations:
trinh nghien » trinh nghe, kinh nghiem, trinh thiet
nghe duoc » nghiem duoc, nghe nuoi, che duoc
sach thi » sach thu, sach tai, sach thieu
thi nghe » thai nghe, thi nghiem, thi ngoc
duoc hoc » quoc hoi
su sach » so sach
vu sach » vu bach, vu khach
d hoc » du hoc, ad hoc, de hoc

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: (( su sach thi nghe duoc hoc ) OR ( vu sach ((trac nghiem) OR (trinh nghien)) d hoc ))~.
• Adding a wildcard symbol may retrieve word variants: (( su sach thi nghe duoc hoc ) or ( vu sach ((trac nghiem) or (trinh nghien)) d hoc ))*.