Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cau tren » cu tren, dau tren, ca tren
toc cao » hoc cao, toc dao, toc co
cuu tre » cau treo
sach ty » sach y, sach tu, sach thu
cua tre » cua te, cua triet, dua tren
cac toc » cac toi, cac nuoc, cac thoi
qua cac » cua cac
nang ma » tang ma, sang ma, nang cao
ty nang » ky nang, ty xang, ty hang
cao do » cao dao, cau do, cap do
do va » do van

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 ty nang ma hoa. hieu qua cac toc cao do va ((((cuu tre) or (cau tren))) or (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty nang ma hoa. hieu qua cac toc cao do va ((((cuu tre) OR (cau tren))) OR (cua tre)).
• Adding a wildcard symbol may retrieve word variants: toc sach ty nang ma hoa. hieu qua cac toc cao do va ((((cuu tre) or (cau tren))) or (cua tre))*.