Perhaps you should try some spelling variations:
va nghiem » van nghiem, va nghien, va nghiep
thu sach » tu sach, thuat sach, thuoc sach
sach dat » sach dao, sach danh, sach bai
dat nghe » day nghe, da nghe, dang nghe
hoach va » hoach xay, hanh va, doanh va
su hoc » tu hoc, du hoc, su ho
so hoc » co hoc, mo hoc, so hoa
d hoc » du hoc, de hoc, y hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( thu sach dat nghe ((d hoc) or (ad hoc)) ) or ( thu hoach va nghiem ((su hoc) or (so hoc)) ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( thu sach dat nghe ((d hoc) OR (ad hoc)) ) OR ( thu hoach va nghiem ((su hoc) OR (so hoc)) )).
• Adding a wildcard symbol may retrieve word variants: (( thu sach dat nghe ((d hoc) or (ad hoc)) ) or ( thu hoach va nghiem ((su hoc) or (so hoc)) ))*.