Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
toc sach » hoc sach, doc sach, thuoc sach
ban hanh » ban hang
hanh va » hang va, hanh vi
duc ban » duc tan, duc van, dua ban
cau duc » cao duc, cau luc, chu duc
van cau » van dau, van hau, van chat
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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