Perhaps you should try some spelling variations:
canh trac » canh tac, anh trac, canh tranh
sach trac » sach truc, sach tranh, sach tham
nghiem d » nghiem de, nghiem _, nghiem h
tu canh » thu canh, tu chanh, tu can
so sach » so sanh, bo sach, co sach
de hoc » te hoc, dien hoc
du hoc » tu hoc, duoc hoc
d hoc » ad hoc, y hoc, _ hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu canh trac nghiem ((de hoc) or (du hoc)) ) or ( so sach trac nghiem d hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu canh trac nghiem ((de hoc) OR (du hoc)) ) OR ( so sach trac nghiem d hoc )).
• Adding a wildcard symbol may retrieve word variants: (( tu canh trac nghiem ((de hoc) or (du hoc)) ) or ( so sach trac nghiem d hoc ))*.