Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
hanh di » hanh vi, hanh de, hang di
va hanh » van hanh, va thanh, va danh
cam duc » cam xuc, cao duc, pham duc
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
va nang » van nang, da nang, cam nang
va cam » va cham, va cac, va cao
di cua » dai cua, doi cua, de cua
o hoc » co hoc, mo hoc, so hoc
o hoi » co hoi, o hai, o hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (hoc sach)) va nang ((o hoi) OR (o hoc)). hieu va cam duc va hanh di cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) va nang ((o hoi) OR (o hoc)). hieu va cam duc va hanh di cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (hoc sach)) va nang ((o hoi) OR (o hoc)). hieu va cam duc va hanh di cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) va nang ((o hoi) OR (o hoc)). hieu va cam duc va hanh di cua tre*.