Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
xa dinh » xac dinh, va dinh, ba dinh
dinh ca » dinh cac, dinh cua, dinh cao
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
me hoi » le hoi
cac tu » cac thu, cach tu, tac tu
ca cua » co 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 y nang ((me hoi) or (ma hoa)). hieu va ((cac tu) OR (cac du)) xa dinh ca cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y nang ((me hoi) OR (ma hoa)). hieu va ((cac tu) OR (cac du)) xa dinh ca cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y nang ((me hoi) or (ma hoa)). hieu va ((cac tu) OR (cac du)) xa dinh ca cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y nang ((me hoi) or (ma hoa)). hieu va ((cac tu) OR (cac du)) xa dinh ca cua tre*.