Perhaps you should try some spelling variations:
hieu cac » hieu luc, hieu van, vien cac
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
giai va » giai van, gia va, giai ma
va dinh » van dinh, va kinh, va tinh
dinh va » dinh van, dinh ve, tinh va
cua tre » cuu tre, cua triet, dua tren
cua te » cua tu

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang xa hoi. hieu ((hieu cac) OR (hieu va)) giai va dinh va ((cua tre) OR (cua te))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang xa hoi. hieu ((hieu cac) OR (hieu va)) giai va dinh va ((cua tre) or (cua te))~".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. hieu ((hieu cac) OR (hieu va)) giai va dinh va ((cua tre) or (cua te))*.