Perhaps you should try some spelling variations:
hieu hien » bieu hien, dieu hien, chieu chien
hieu vien » hieu viec, thieu nien, hieu tieng
trinh vi » trinh va, trinh ve, trinh viet
cac dai » cac dan, cac bai, can dai
tinh vi » tinh voi, tinh va, dinh vi
su sach » so sach, vu sach
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
dai va » mai va
nang o » nang co, nang ho, nang ro
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: su sach ky nang o hoi. ((hieu vien) or (hieu hien)) cac dai va ((tinh vi) OR (trinh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang o hoi. ((hieu vien) OR (hieu hien)) cac dai va ((tinh vi) OR (trinh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang o hoi. ((hieu vien) or (hieu hien)) cac dai va ((tinh vi) OR (trinh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang o hoi. ((hieu vien) or (hieu hien)) cac dai va ((tinh vi) OR (trinh vi)) cua tre*.