Perhaps you should try some spelling variations:
hieu viec » nhieu viec, hieu ve, sieu viet
hanh thai » nhanh thai, hinh thai, hanh tai
hieu vien » hieu hien, thieu nien, hieu tieng
thai cua » than cua, tai cuc, tri cua
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
luc van » luoc van, luu van, duc van
cac luc » cau luc, coc luc, cac nuoc
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
co hoi » co hoc, co loi
o hoi » o hoc, o hai, o hoa

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