Perhaps you should try some spelling variations:
doan thi » dan thi, doanh tai, hoang thi
tu sach » thu sach, su sach, te sach
cac toi » cac thoi
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ty hang » ly hang, ty xang, thi hang
ty lang » tay lang, ty xang, tu lang
toi va » thoi va, tuoi va, hoi va
dan vi » doan vi, don vi, dan va
ve cac » va cac, vien cac

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 hang)) xa hoi. hieu ve cac toi 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 hang)) xa hoi. hieu ve cac toi va ((dan vi) OR (doan thi)) cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty lang) or (ty hang)) xa hoi. hieu ve cac toi va ((dan vi) or (doan thi)) cua tre*.