Perhaps you should try some spelling variations:
cac quoc » cac cuoc, cao quoc, han quoc
sach thu » sach thue, sach thieu, sach tham
manh hai » lanh hai, minh hai, thanh hai
ban manh » ban hanh, van manh, ban mach
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hai cua » thai cua, dai cua, hoi cua
tu sach » thu sach, su sach, te sach
lang xa » lang ha, dang xay, lang van
nang xa » nang x, nang ma, mang xa
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 thu ((nang xa) or (lang xa)) hoi. hieu qua ((cac quoc) OR (cac nuoc)) ban manh hai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu ((nang xa) OR (lang xa)) hoi. hieu qua ((cac quoc) OR (cac nuoc)) ban manh hai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thu ((nang xa) or (lang xa)) hoi. hieu qua ((cac quoc) OR (cac nuoc)) ban manh hai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach thu ((nang xa) or (lang xa)) hoi. hieu qua ((cac quoc) OR (cac nuoc)) ban manh hai cua tre*.