Perhaps you should try some spelling variations:
co sach » bo sach, cuon sach, hoc sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
ve cam » ve cham, ve cac, va cam
xuc va » duc va, tuc va, luc va
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 ky nang ((x hoi) OR (o hoi)). hieu ve cam xuc va hanh vi ((cua tre) or (cuu 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 cam xuc va hanh vi ((cua tre) OR (cuu 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 cam xuc va hanh vi ((cua tre) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: co sach ky nang ((x hoi) OR (o hoi)). hieu ve cam xuc va hanh vi ((cua tre) or (cuu tre))*.