Perhaps you should try some spelling variations:
ban doan » ban doanh, ban dan, ban soan
tu sach » thu sach, su sach, te sach
doan vi » doan va, don vi, doan thi
cuu ban » cuu van, cua ban, cuu san
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
lang ha » long ha
lang xa » dang xay, lang van
ve cac » va cac, vien cac
vi cua » vai cua, di cua
ve cam » ve cham, va cam, ve cai

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