Perhaps you should try some spelling variations:
doan thi » dan thi, doanh tai, hoang thi
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
cac tho » cac thoi, cac tro, cac thu
ty lang » tay lang, ty hang, tu lang
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
tho va » tho van, tao va, tho ca
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) OR (ty xang)) xa hoi. hieu ve cac tho va ((dan vi) or (doan thi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty lang) OR (ty xang)) xa hoi. hieu ve cac tho va ((dan vi) OR (doan thi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty lang) OR (ty xang)) xa hoi. hieu ve cac tho va ((dan vi) or (doan thi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty lang) OR (ty xang)) xa hoi. hieu ve cac tho va ((dan vi) or (doan thi)) cua tre*.