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