Perhaps you should try some spelling variations:
hieu hien » bieu hien, dieu hien, chieu chien
hieu vien » hieu viec, thieu nien, hieu tieng
duoc gia » duoc giao, quoc gia, luoc gia
duc gia » quoc gia
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
cua tre » cua te, cuu tre, cua triet
vi cua » vai cua, di cua

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