Perhaps you should try some spelling variations:
da thanh » dao thanh, dat thanh, dam thanh
so sach » bo sach, co sach, hoc sach
so sanh » do sanh
va nang » van nang, da nang, cam nang
hieu va » lieu va, hieu qua
cac tac » cac toc, cac bac, cac dac
vai cua » dai cua, hai cua, lai cua
vi cua » di cua
x hoi » xa hoi, o hoi, x ho

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

• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (so sanh)) va nang x hoi. hieu va cac tac da thanh ((vi cua) OR (vai cua)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sach) or (so sanh)) va nang x hoi. hieu va cac tac da thanh ((vi cua) OR (vai cua)) tre~".
• Adding a wildcard symbol may retrieve word variants: ((so sach) or (so sanh)) va nang x hoi. hieu va cac tac da thanh ((vi cua) OR (vai cua)) tre*.