Perhaps you should try some spelling variations:
cac quoc » cac nuoc, cac cuoc, cao quoc
hang tai » hang va, dung tai
hanh tai » thanh tai, han tai, hinh tai
quoc lan » quoc ban, nuoc luan, quoc quan
sach ky » sac ky, sach y, sach ty
te sach » toc sach
qua cac » cua cac
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, 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: te sach ky ((nang xa) or (nang ma)) hoi. hieu qua cac quoc lan ((hanh tai) OR (hang tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sach ky ((nang xa) OR (nang ma)) hoi. hieu qua cac quoc lan ((hanh tai) OR (hang tai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach ky ((nang xa) or (nang ma)) hoi. hieu qua cac quoc lan ((hanh tai) OR (hang tai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: te sach ky ((nang xa) or (nang ma)) hoi. hieu qua cac quoc lan ((hanh tai) OR (hang tai)) cua tre*.