Perhaps you should try some spelling variations:
cach dung » sach dung, cach mang, tac dung
thanh hoi » thanh hoai, thanh hoa, thanh hai
ban thanh » ban hanh, ban hang
cach dua » cach cua, cac du, cach de
hoi cua » hoi chuc
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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