Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
thanh va » thanh van, hanh va, thanh ha
luy tre » luyen tre
duc ban » duc tan, duc van, dua ban
ky hang » ky nang, ly hang, ky dang
dau hoi » dai hoi, dan hoi, dau noi
te sac » te sach, te cac, te san
v pham » vi pham, d pham
sac ky » cac ky, sai ky
hieu v » hieu va, hieu ve, hieu 2

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

• Performing a fuzzy search may retrieve terms with similar spellings: te sac ky hang ((dau hoi) or (cau hoi)). hieu v pham duc ban thanh va ((luu tru) or (luy tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sac ky hang ((dau hoi) OR (cau hoi)). hieu v pham duc ban thanh va ((luu tru) OR (luy tre)).
• Adding a wildcard symbol may retrieve word variants: te sac ky hang ((dau hoi) or (cau hoi)). hieu v pham duc ban thanh va ((luu tru) or (luy tre))*.