Perhaps you should try some spelling variations:
van thanh » ban thanh, van tuan
thanh vi » hanh vi, thanh va, thanh ve
hieu va » lieu va, hieu qua
sach ky » sach y, sach ty, sach kem
hieu ve » hieu van
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
sac ky » cac ky, sai ky
bac vo » bac bo, bac ho, bac va
vi cua » vai cua, di cua
o hoi » co hoi, o hoc, o hai

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) or (sac ky)) nang o hoi. ((hieu ve) OR (hieu va)) bac vo van thanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sac ky)) nang o hoi. ((hieu ve) OR (hieu va)) bac vo van thanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (sac ky)) nang o hoi. ((hieu ve) OR (hieu va)) bac vo van thanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sac ky)) nang o hoi. ((hieu ve) OR (hieu va)) bac vo van thanh vi cua tre*.