Perhaps you should try some spelling variations:
thanh dai » thanh hai, thanh tai, thanh dat
van thanh » ban thanh, van tuan
hieu van » hieu va, thien van, lieu va
cac cach » cai cach, cuoc cach, va cach
tu sach » thu sach, su sach, te sach
cac cac » ca cac, cac bac, cac cam
cua tre » cua te, cuu tre, cua triet
sach v » sach va, sach y, sach 2
v nang » va nang, vu nang, van nang
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: tu sach v nang ((x hoi) OR (o hoi)). hieu van ((cac cac) or (cac cach)) van thanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach v nang ((x hoi) OR (o hoi)). hieu van ((cac cac) OR (cac cach)) van thanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach v nang ((x hoi) OR (o hoi)). hieu van ((cac cac) or (cac cach)) van thanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach v nang ((x hoi) OR (o hoi)). hieu van ((cac cac) or (cac cach)) van thanh dai cua tre*.