Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
hieu va » lieu va, hieu qua
cac tac » cac toc, cac bac, cac dac
lang xa » lang ha, dang xay, lang van
dang xa » dang xay, dang ha, dang va
cua tre » cua te, cuu tre, cua triet
tac va » tac da, tac xa, tuc va
do van » dao van, vo van, so van

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