Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
thanh dai » thanh hai, thanh tai, thanh dat
hieu van » hieu va, thien van, lieu va
su sach » so sach
vu sach » vu bach, vu khach
van bac » van ban, van bao, van hac
bac dai » bach mai
dai ban » dai han, tai ban, di ban
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
x hoi » xa hoi, o hoi, 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: ((su sach) or (vu sach)) y nang ((x hoi) OR (x ho)). hieu van bac dai ban thanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (vu sach)) y nang ((x hoi) OR (x ho)). hieu van bac dai ban thanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (vu sach)) y nang ((x hoi) OR (x ho)). hieu van bac dai ban thanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (vu sach)) y nang ((x hoi) OR (x ho)). hieu van bac dai ban thanh dai cua tre*.