Perhaps you should try some spelling variations:
dung doi » huong doi, dung tai, dung co
sang mai » sang ma, sang tai, lang mai
su sach » vu sach
doi cua » dai cua, hoi cua
xa dung » xay dung, xa dong, va dung
cac tuc » cac toc, cac tu, cac tac
hieu va » lieu va, hieu qua
hieu ve » hieu van
mai hoi » mai khoi, dai hoi, lai hoi
ky sang » ky nang, ky dang, ky tang
so sach » so sanh, bo sach, co sach
cua tre » cua te, cuu tre, cua triet

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