Perhaps you should try some spelling variations:
hieu vien » hieu viec, thieu nien, hieu tieng
hieu hien » bieu hien, dieu hien, chieu chien
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
cac tu » cac thu, cach tu, cac du
dan vi » doan vi, dan va, gan vi
x hoi » xa hoi, o hoi, x ho

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 x hoi. ((hieu vien) OR (hieu hien)) cac tu va ((dan vi) or (don vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang x hoi. ((hieu vien) OR (hieu hien)) cac tu va ((dan vi) OR (don vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang x hoi. ((hieu vien) OR (hieu hien)) cac tu va ((dan vi) or (don vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang x hoi. ((hieu vien) OR (hieu hien)) cac tu va ((dan vi) or (don vi)) cua tre*.