Perhaps you should try some spelling variations:
su sach » so sach, vu sach
ky sang » ky dang, ky tang, duy sang
dai hoi » dai hoc, dai hai, dai moi
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
vai cua » dai cua, lai cua, bai cua
hai cua » thai cua, dai cua, hoi cua
cac tu » cac thu, cach tu, cac du

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