Perhaps you should try some spelling variations:
cac thoi » cac toi, cac hop, cac tro
te sach » toc sach
sach ky » sac ky, sach y, sach ty
cac toc » cac toi, cac nuoc
nam dan » nam dinh
dan sai » danh sai, doan sai, dan tai
sai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: te sach ky nang x ho. ((hieu qua) OR (lieu va)) ((cac toc) OR (cac thoi)) nam dan sai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach ky nang x ho. ((hieu qua) or (lieu va)) ((cac toc) OR (cac thoi)) nam dan sai cua tre~".
• Adding a wildcard symbol may retrieve word variants: te sach ky nang x ho. ((hieu qua) or (lieu va)) ((cac toc) OR (cac thoi)) nam dan sai cua tre*.