Perhaps you should try some spelling variations:
tinh vai » tinh va, tinh hai, tinh bai
su sach » so sach, vu sach
vai cua » dai cua, hai cua, lai cua
va tinh » may tinh
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu van
ty hang » ly hang, ty xang, thi hang
ty tang » tay tang, ty xang, ky tang
luc va » duc va, tuc va, loc va

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ((ty tang) or (ty hang)) xa hoi. ((hieu ve) OR (hieu va)) coc luc va tinh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((ty tang) OR (ty hang)) xa hoi. ((hieu ve) OR (hieu va)) coc luc va tinh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((ty tang) or (ty hang)) xa hoi. ((hieu ve) OR (hieu va)) coc luc va tinh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ((ty tang) or (ty hang)) xa hoi. ((hieu ve) OR (hieu va)) coc luc va tinh vai cua tre*.