Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
cau tren » cu tren, dau tren, ca tren
vien cac » vien bach, vien dai, vien da
sach ty » sach y, sach tu, sach thu
ty nang » ky nang, ty xang, ty hang
cuu tre » cua tre, cau treo
tu sach » thu sach, su sach, te sach
cac su » cach su, cac sau, cac du
va dao » ca dao
dao ve » bao ve, dap ve, dau ve
o hoi » co hoi, o hoc, o hoa
o hai » co hai, so hai, o lai
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 vien 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 vien 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 vien cac su va dao ve ((cuu tre) or (cau tren))*.