Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
hieu van » hieu va, thien van, lieu va
van cach » va cach, van canh, vat cach
cach su » cach tu, hoach su
cuu tre » cua tre, cau treo
su sach » so sach, vu sach
co hoi » co hoc, co loi
y nang » ky nang, ly nang, v nang
va dao » ca dao
dao ve » bao ve, dap ve, dau ve
o lai » o lao
su va » su van, tu va

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 y nang ((co hoi) or (o lai)). hieu van cach su va dao ve ((cuu tre) or (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((co hoi) OR (o lai)). hieu van cach su va dao ve ((cuu tre) OR (cau tren)).
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((co hoi) or (o lai)). hieu van cach su va dao ve ((cuu tre) or (cau tren))*.