Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien cac » vien bach, vien dai, vien da
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
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua
5 hoi » o hoi

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 ((5 hoi) or (xa hoi)). hieu vien cac tu va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((5 hoi) OR (xa hoi)). hieu vien cac tu va dan vi cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((5 hoi) or (xa hoi)). hieu vien cac tu va dan vi cua tre*.