Perhaps you should try some spelling variations:
nuoc ban » nuoc san, quoc ban, buoc ban
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
chua tre » chua tri, cua tre, chua trieu
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
anh vua » anh va, anh cua, anh tuan
ve cac » va cac, vien cac
anh vu » hanh vu, anh tu, anh va

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 ky) or (cac ky)) nang x ho. hieu ve cac nuoc ban ((anh vua) OR (anh vu)) chua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (cac ky)) nang x ho. hieu ve cac nuoc ban ((anh vua) OR (anh vu)) chua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (cac ky)) nang x ho. hieu ve cac nuoc ban ((anh vua) OR (anh vu)) chua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (cac ky)) nang x ho. hieu ve cac nuoc ban ((anh vua) OR (anh vu)) chua tre*.