Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
hanh va » hang va
duc van » duc va, duc tan, duc manh
cao duc » dao duc, cao suc, giao duc
van cao » van dao, van bao, van hao
cua tre » cua te, cuu tre, cua triet
sach ky » sach y, sach ty, sach kem
sac ky » cac ky, sai ky
x hoi » xa hoi, o hoi, x ho

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach ky) or (sac ky)) nang x hoi. hieu van cao duc van ((hanh va) OR (hanh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ky) OR (sac ky)) nang x hoi. hieu van cao duc van ((hanh va) OR (hanh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) or (sac ky)) nang x hoi. hieu van cao duc van ((hanh va) OR (hanh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach ky) or (sac ky)) nang x hoi. hieu van cao duc van ((hanh va) OR (hanh vi)) cua tre*.