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
va dinh » van dinh, va kinh, va tinh
dinh va » dinh van, dinh ve, tinh va
cua tre » cua te, cuu tre, cua triet
lao va » tao va, cao va, bao va
va cua » va chua, via cua, ca cua

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 nang xa hoi. hieu ((hieu cac) OR (hieu va)) lao va dinh va cua tre~.
• 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)) lao va dinh va cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang xa hoi. hieu ((hieu cac) OR (hieu va)) lao va dinh va cua tre*.