Perhaps you should try some spelling variations:
hanh thai » nhanh thai, hinh thai, hanh tai
hieu van » hieu va, thien van, lieu va
thai cua » than cua, tai cuc, tri cua
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
cac duc » cao duc, cac dac, cac nuoc
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va
nang o » nang co, nang ho, nang ro
o hai » co hai, so hai, o lai

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