Perhaps you should try some spelling variations:
dinh viet » ninh viet, danh viet, trinh viet
su sach » so sach, vu sach
cac toc » cac toi, cac nuoc, cac thoi
dinh vi » dinh ve, dinh tri, dinh thi
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
lang xa » lang ha, dang xay, lang van
toc va » hoc va, toc ta, tuc va
ve cac » va cac, vien cac

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 ((van xay) or (lang xa)) hoi. hieu ve cac toc va ((dinh vi) OR (dinh viet)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((van xay) OR (lang xa)) hoi. hieu ve cac toc va ((dinh vi) OR (dinh viet)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((van xay) or (lang xa)) hoi. hieu ve cac toc va ((dinh vi) OR (dinh viet)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((van xay) or (lang xa)) hoi. hieu ve cac toc va ((dinh vi) OR (dinh viet)) cua tre*.