Perhaps you should try some spelling variations:
kmay nang » ky nang, kha nang, may nong
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
may nang » may nong, ky nang, cam nang
vat cua » mat cua, bat cua, dat cua
van vat » van chat, nhan vat
cac tac » cac toc, cac bac, cac dac
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
tac xa » tuc xa, tac da
xa van » va van, ha van, ma van
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: ((toc sach) OR (hoc sach)) ((may nang) or (kmay nang)) o hoi. hieu va cac tac xa van vat cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ((may nang) OR (kmay nang)) o hoi. hieu va cac tac xa van vat cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (hoc sach)) ((may nang) or (kmay nang)) o hoi. hieu va cac tac xa van vat cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) ((may nang) or (kmay nang)) o hoi. hieu va cac tac xa van vat cua tre*.