Perhaps you should try some spelling variations:
hanh thai » nhanh thai, hinh thai, anh thai
hanh tai » thanh tai, hang tai, han tai
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
cac duc » cac du, cao duc, cac dac
duc van » duc va, duc tan, duc manh
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va
cua tre » cua te, cuu tre, cua triet
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 van ((hanh thai) OR (hanh tai)) 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 van ((hanh thai) OR (hanh tai)) 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 van ((hanh thai) OR (hanh tai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang o hai. ((hieu ve) or (hieu van)) cac duc van ((hanh thai) OR (hanh tai)) cua tre*.