Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
cuu tre » cua tre, cau treo
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va, hieu van
tu sach » thu sach, su sach, te sach
ty nang » ky nang, ty xang, ty hang
cac su » cach su, cac sau, cac du
va dao » ca dao
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
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: tu sach ty nang ((o hoi) OR (o hai)). hieu ve cac su va dao ve ((cuu tre) or (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang ((o hoi) OR (o hai)). hieu ve cac su va dao ve ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty nang ((o hoi) OR (o hai)). hieu ve cac su va dao ve ((cuu tre) or (cau tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang ((o hoi) OR (o hai)). hieu ve cac su va dao ve ((cuu tre) or (cau tren))*.