Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh vai » hanh vi, hanh va, hanh tai
nam thuc » nam thuoc, am thuc, nam thu
su sach » so sach, vu sach
hieu va » lieu va, hieu qua
vai cua » dai cua, hai cua, lai cua
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu van
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang

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) or (toc sach)) ky lang xa hoi. ((hieu ve) OR (hieu va)) nam thuc va hanh vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (toc sach)) ky lang xa hoi. ((hieu ve) OR (hieu va)) nam thuc va hanh vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (toc sach)) ky lang xa hoi. ((hieu ve) OR (hieu va)) nam thuc va hanh vai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (toc sach)) ky lang xa hoi. ((hieu ve) OR (hieu va)) nam thuc va hanh vai cua tre*.