Perhaps you should try some spelling variations:
dua tren » dung tren
nam thuc » nam thuoc, am thuc, nam thu
sach ky » sac ky, sach y, sach ty
cu tren » tu tren
hang di » hang doi, hang vi, hang dien
va hang » van hang, va nang, va lang
tu sach » thu sach, su sach, te sach
nam luc » nang luc, nhan luc, nam duoc
hieu va » lieu va, hieu qua
tang xa » trang xa, tang ma, lang xa
ky tang » ky nang, ky dang, kho tang

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 ky tang xa hoi. hieu va ((nam luc) or (nam thuc)) va hang di ((cu tren) or (dua tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang xa hoi. hieu va ((nam luc) OR (nam thuc)) va hang di ((cu tren) OR (dua tren)).
• Adding a wildcard symbol may retrieve word variants: tu sach ky tang xa hoi. hieu va ((nam luc) or (nam thuc)) va hang di ((cu tren) or (dua tren))*.