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, do tang, de thanh
de dang » da dang, le dang, do dang
thai va » thai van
ve cao » va cao, ve bao, ve cac
hai va » hai van, hoi va, mai 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 dang) or (de tang)) xa hoi. hieu ve cao duc va hanh ((hai va) OR (thai va)) thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ((de dang) OR (de tang)) xa hoi. hieu ve cao duc va hanh ((hai va) OR (thai va)) thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ((de dang) or (de tang)) xa hoi. hieu ve cao duc va hanh ((hai va) OR (thai va)) thiet".
• Adding a wildcard symbol may retrieve word variants: su sach ((de dang) or (de tang)) xa hoi. hieu ve cao duc va hanh ((hai va) OR (thai va)) thiet*.