Perhaps you should try some spelling variations:
sach tranh » canh tranh
tranh nghe » trinh nghe, anh nghe, hanh nghe
sach trac » sach truc, sach tham, sach tren
nghe duoc » nghiem duoc, nghe nuoi, che duoc
duoc hoc » quoc hoi
so sach » so sanh, bo sach, co sach
tu hoc » te hoc

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( so sach trac nghiem ((du hoc) OR (tu hoc)) ) or ( so sach tranh nghe duoc hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( so sach trac nghiem ((du hoc) OR (tu hoc)) ) OR ( so sach tranh nghe duoc hoc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( so sach trac nghiem ((du hoc) OR (tu hoc)) ) or ( so sach tranh nghe duoc hoc ))".
• Adding a wildcard symbol may retrieve word variants: (( so sach trac nghiem ((du hoc) OR (tu hoc)) ) or ( so sach tranh nghe duoc hoc ))*.