Perhaps you should try some spelling variations:
nang cai » nang cao, nang tai, nang cap
hieu van » hieu va, thien van, lieu va
hanh vai » hanh vi, hanh va, hanh tai
so sach » so sanh, bo sach, co sach
cai hoi » cau hoi, dai hoi, cai hoa
hieu ve » hieu va
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
xuc va » tuc va, luc va, xac va

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang cai hoi. ((hieu ve) or (hieu van)) cam ((xuc va) OR (duc va)) hanh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang cai hoi. ((hieu ve) OR (hieu van)) cam ((xuc va) OR (duc va)) hanh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y nang cai hoi. ((hieu ve) or (hieu van)) cam ((xuc va) OR (duc va)) hanh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach y nang cai hoi. ((hieu ve) or (hieu van)) cam ((xuc va) OR (duc va)) hanh vai cua tre*.