Perhaps you should try some spelling variations:
cac quoc » cac nuoc, cac cuoc, cao quoc
hieu cua » hieu qua, dieu cua, bieu cua
lanh hai » manh hai, thanh hai, lang chai
quoc ban » quoc bao, quoc lan, quoc quan
anh hai » manh hai, anh thai, anh bai
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
lang xa » lang ha, dang xay, lang van
mang xa » mang may, dang xay, mang cua
cua tre » cua te, cuu tre, cua triet

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 ((mang xa) or (lang xa)) hoi. hieu cua cac quoc ban ((anh hai) or (lanh hai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((mang xa) OR (lang xa)) hoi. hieu cua cac quoc ban ((anh hai) OR (lanh hai)) cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ty ((mang xa) or (lang xa)) hoi. hieu cua cac quoc ban ((anh hai) or (lanh hai)) cua tre*.