Perhaps you should try some spelling variations:
hieu tieng » viet tieng, dien tieng, tiep tieng
hieu hien » bieu hien, dieu hien, chieu chien
tu sach » thu sach, su sach, te sach
ty nang » ky nang, ty hang, ly nang
cac bac » cac bai, cac ban, cac cach
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
bac va » ban va, bac ha, bao va
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 ((ty nang) OR (ty xang)) xa hoi. ((hieu tieng) or (hieu hien)) cac bac va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty nang) OR (ty xang)) xa hoi. ((hieu tieng) OR (hieu hien)) cac bac va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty nang) OR (ty xang)) xa hoi. ((hieu tieng) or (hieu hien)) cac bac va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty nang) OR (ty xang)) xa hoi. ((hieu tieng) or (hieu hien)) cac bac va hanh vi cua tre*.