Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
cac toc » cac toi, cac nuoc, cac thoi
cac tuc » cac tu, cac tac, cac nuoc
sach ty » sach y, sach tu, sach thu
hieu va » lieu va, hieu qua
hieu ve » hieu van
nang ma » tang ma, sang ma, nang cao
ty nang » ky nang, ty xang, ty hang
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
va don » va dong, va doc, va do
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 ma hoi. ((hieu ve) or (hieu va)) ((cac tuc) or (cac toc)) va don vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang ma hoi. ((hieu ve) OR (hieu va)) ((cac tuc) OR (cac toc)) va don vi cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang ma hoi. ((hieu ve) or (hieu va)) ((cac tuc) or (cac toc)) va don vi cua tre*.