Perhaps you should try some spelling variations:
sach trach » sach tranh, sach truc, sat trach
khach trac » khach trai, khanh trach, khac trai
tri khach » thi khanh
toc sach » hoc sach, doc sach, thuoc sach
nhiem d » nghiem d, nghiem de, nghiem do
d hoc » du hoc, ad hoc, de hoc
nghiem » nghiep, nghien

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( toc sach trach nhiem d hoc ) or ( tri khach trac nghiem ngu hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( toc sach trach nhiem d hoc ) OR ( tri khach trac nghiem ngu hoc )).
• Adding a wildcard symbol may retrieve word variants: (( toc sach trach nhiem d hoc ) or ( tri khach trac nghiem ngu hoc ))*.