Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
doan vi » doan va, don vi, doan thi
hieu ve » hieu va, hieu van
cac thu » cach thuc, cac thoi
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
thu va » thuc va, thue va, tu va
dan vi » don vi, dan va, gan vi

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