Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
cuu tre » cua tre, cau tren, cau treo
cac tu » cac thu, cach tu, tac tu
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cuu » vi luu, vinh cuu
o hoi » co hoi, o hoc, o hai

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 (xa hoi)). hieu ve ((cac tu) or (cac du)) va dan vi cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoi) OR (xa hoi)). hieu ve ((cac tu) OR (cac du)) va dan vi cuu tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoi) or (xa hoi)). hieu ve ((cac tu) or (cac du)) va dan vi cuu tre*.