Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
hanh di » hanh vi, hanh de, hang di
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
v lang » va lang, o lang, van lang
_ lang » o lang, _ land
du va » dau va, tu va, su va

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

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