Perhaps you should try some spelling variations:
va nghiem » van nghiem, va nghien, va nghiep
nghiem so » nghiem son, nghiep so, nghiem do
thu sach » thuat sach, thuoc sach, khau sach
bai nghe » thai nghe, van nghe, nam nghe
hoach va » hoach xay, hanh va, doanh va
tu sach » su sach, te sach, tu cach
du hoc » duoc hoc
tu hoc » te hoc
so hoc » co hoc, mo hoc, so hoa

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

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