Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cao hoi » cau hoi, cao hoc, tao hoi
hieu ve » hieu va, hieu van
cac tac » cac toc, cac bac, cac dac
co hoi » co hoc, co loi
ve cac » va cac, vien cac
va dau » va dao
ca dan » cac dan, ca dao
ca cau » cua cau, cac cau, can cau

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 ((cao hoi) OR (co hoi)). hieu ve cac tac ((va dau) or (ca dan)) ca cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((cao hoi) OR (co hoi)). hieu ve cac tac ((va dau) OR (ca dan)) ca cau tren*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((cao hoi) OR (co hoi)). hieu ve cac tac ((va dau) or (ca dan)) ca cau tren*".