Perhaps you should try some spelling variations:
thanh di » thanh doi, thanh de, thanh dinh
thanh do » thanh de, thanh pho, thanh hoa
tu sach » thu sach, su sach, te sach
cao hoi » co hoi, cao hoc, tao hoi
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang

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