Perhaps you should try some spelling variations:
cac thoi » cac toi, cac hop, cac tro
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
hieu ve » hieu va, hieu van
cac toc » cac toi, cac nuoc
da nang » cam nang, kha nang, cao nang
thiet » thieu

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 lang xa hoi. hieu ve ((cac toc) OR (cac thoi)) ((van dong) or (da nang)) hoi va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky lang xa hoi. hieu ve ((cac toc) OR (cac thoi)) ((van dong) OR (da nang)) hoi va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky lang xa hoi. hieu ve ((cac toc) OR (cac thoi)) ((van dong) or (da nang)) hoi va thiet".
• Adding a wildcard symbol may retrieve word variants: su sach ky lang xa hoi. hieu ve ((cac toc) OR (cac thoi)) ((van dong) or (da nang)) hoi va thiet*.