Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh dai » hanh tai, hanh dao, vanh dai
va hanh » van hanh, va thanh, va danh
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
va lang » va nang, hoa lang
o lang » hoa lang, hoi lang
cam lo » nam lo, cam ly
cam o » cham o, ca o, tam o

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