Perhaps you should try some spelling variations:
su sach » so sach, vu sach
va hanh » van hanh, va thanh, va danh
cao duc » dao duc, cao suc, giao duc
hieu ve » hieu va, hieu van
de tang » le tang, de dang, do tang
de mang » ke mang, de dang, de bang
ve cao » va cao, ve bao, ve cac
va dan » ca dan, va dao, va dau
hai va » hai van, thai va, hoi va
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 ((de mang) or (de tang)) xa hoi. hieu ve cao duc ((va hanh) or (va dan)) hai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((de mang) OR (de tang)) xa hoi. hieu ve cao duc ((va hanh) OR (va dan)) hai va thiet.
• Adding a wildcard symbol may retrieve word variants: su sach ((de mang) or (de tang)) xa hoi. hieu ve cao duc ((va hanh) or (va dan)) hai va thiet*.