Perhaps you should try some spelling variations:
co sach » bo sach, cuon sach, hoc sach
vai cua » dai cua, hai cua, lai cua
va danh » va dinh, va dan, va hanh
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
ban bo » can bo, ban do, ban co
vi cua » di cua
ve ban » te ban, va ban, ve bao
o hoi » co hoi, o hoc, o hai
bo va » bao va, do va, so va
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: co sach ky nang ((x hoi) OR (o hoi)). hieu ve ban bo va danh ((vi cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: co sach ky nang ((x hoi) OR (o hoi)). hieu ve ban bo va danh ((vi cua) OR (vai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "co sach ky nang ((x hoi) OR (o hoi)). hieu ve ban bo va danh ((vi cua) or (vai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: co sach ky nang ((x hoi) OR (o hoi)). hieu ve ban bo va danh ((vi cua) or (vai cua)) tre*.