Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
cau thuc » cuu thuc, can thuc, cau phuc
su sach » so sach, vu sach
hanh te » hanh tu, hanh ve, hanh de
sach va » sach xa, sach ha, sach dao
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
va nang » van nang, da nang, cam nang
te cua » tue cua, le cua, de 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: su sach va nang ((x hoi) or (o hoi)). hieu ve ((cau thuc) or (cau truc)) van hanh te cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach va nang ((x hoi) OR (o hoi)). hieu ve ((cau thuc) OR (cau truc)) van hanh te cua tre.
• Adding a wildcard symbol may retrieve word variants: su sach va nang ((x hoi) or (o hoi)). hieu ve ((cau thuc) or (cau truc)) van hanh te cua tre*.