Perhaps you should try some spelling variations:
sach hay » sach han, sach ha, sach nay
hay lang » ha lang, tay lang, nhan lang
doan thi » dan thi, doanh tai, hoang thi
tu sach » thu sach, su sach, te sach
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
cac tho » cac thoi, cac tro, cac thu
lang xa » lang ha, dang xay, lang van
ve cac » va cac, vien cac
dan va » doan va, dan ca, ban va
dan vi » doan vi, don vi, 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 hay lang xa hoi. hieu ve cac tho ca ((((dan vi) or (dan va))) or (doan thi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach hay lang xa hoi. hieu ve cac tho ca ((((dan vi) OR (dan va))) OR (doan thi)) cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach hay lang xa hoi. hieu ve cac tho ca ((((dan vi) or (dan va))) or (doan thi)) cua tre*.