Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien dai » hien dai
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
dai tu » dai thu, tai tu, mai tu
dan vi » doan vi, dan va, gan vi
x hoi » o hoi, x ho, 5 hoi

You may be able to get more results by adjusting your search query.

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