Perhaps you should try some spelling variations:
ban thanh » ban hang
ban hanh » ban hang
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
nam duc » nam duoc, pham duc, nam thuc
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
va nam » van nam, ha nam, va nay
x hoi » xa hoi, o hoi, x ho

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 hoi. hieu va nam duc ((ban thanh) OR (ban hanh)) vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (cac ky)) nang x hoi. hieu va nam duc ((ban thanh) OR (ban hanh)) vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (cac ky)) nang x hoi. hieu va nam duc ((ban thanh) OR (ban hanh)) vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (cac ky)) nang x hoi. hieu va nam duc ((ban thanh) OR (ban hanh)) vai cua tre*.