Perhaps you should try some spelling variations:
quoc quan » qua quan, luc quan, hoc quan
tang van » dang van, hoang van, trong van
quoc ban » quoc bao, quoc lan, quoc binh
banh dai » benh dai, ban dai, vanh dai
tu sach » thu sach, su sach, te sach
nang xa » nang x, lang xa, nang ma
qua cac » cua cac
cua tre » cua te, cuu tre, cua triet

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang xa) OR (tang van)) hoi. hieu qua cac ((quoc ban) OR (quoc quan)) banh dai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang xa) or (tang van)) hoi. hieu qua cac ((quoc ban) OR (quoc quan)) banh dai cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang xa) or (tang van)) hoi. hieu qua cac ((quoc ban) OR (quoc quan)) banh dai cua tre*.