Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
cuu tre » cua tre, cau treo
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
tu sach » thu sach, su sach, te sach
cac su » cach su, cac sau, cac du
su van » tu van, vu van
dao ve » bao ve, dap ve, dau ve
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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