Perhaps you should try some spelling variations:
co sach » bo sach, cuon sach, hoc sach
sach tu » sach thu, cach tu, sach ty
tu nang » tru nang, tu nong, tu nano
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
va danh » va dinh, va dan, va hanh
vai cua » dai cua, lai cua, bai cua
hai cua » thai cua, dai cua, hoi cua
x hoi » xa hoi, x ho, 5 hoi
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: co sach tu nang ((x hoi) or (o hoi)). hieu ve pham duc va danh ((vai cua) OR (hai cua)) te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: co sach tu nang ((x hoi) OR (o hoi)). hieu ve pham duc va danh ((vai cua) OR (hai cua)) te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "co sach tu nang ((x hoi) or (o hoi)). hieu ve pham duc va danh ((vai cua) OR (hai cua)) te".
• Adding a wildcard symbol may retrieve word variants: co sach tu nang ((x hoi) or (o hoi)). hieu ve pham duc va danh ((vai cua) OR (hai cua)) te*.