Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va, hieu van
lang ha » long ha
lang xa » dang xay, lang van
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
tro va » tao va, tho va, tro ba
dan vi » doan vi, don vi, dan va

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 ((lang xa) or (lang ha)) hoi. hieu ve cac tro va ((dan vi) or (doanh tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((lang xa) OR (lang ha)) hoi. hieu ve cac tro va ((dan vi) OR (doanh tai)) cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ty ((lang xa) or (lang ha)) hoi. hieu ve cac tro va ((dan vi) or (doanh tai)) cua tre*.