Perhaps you should try some spelling variations:
vien dai » hien dai
vien cac » vien bach, vien da, gian cac
su sach » so sach, vu sach
tai cua » thai cua, tai cuc, tri cua
dan tai » van tai, dan thi, han tai
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
nang xa » nang x, lang xa, nang ma
bo va » bao va, do va, co va
so va » so van, so vat, su va

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 xa hoi. hieu ((vien cac) or (vien dai)) ((bo va) OR (so va)) dan tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang xa hoi. hieu ((vien cac) OR (vien dai)) ((bo va) OR (so va)) dan tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang xa hoi. hieu ((vien cac) or (vien dai)) ((bo va) OR (so va)) dan tai cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang xa hoi. hieu ((vien cac) or (vien dai)) ((bo va) OR (so va)) dan tai cua tre*.