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
van manh » van minh, van anh, van hanh
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)) van 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)) van 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)) van manh hai cua tre*.