Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
tai cuu » tai cuc, tai buu, tai cua
dan tai » van tai, dan thi, han tai
thuc va » thuc vat, thuc dan, thuc day
cuu tre » cua tre, cau tren, cau treo
tang xa » trang xa, tang ma, lang xa
ky tang » ky nang, ky dang, kho tang
va nay » va ngay, va cay
va dan » ca dan, va dao, va dau
va nam » van nam, ha nam

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 (doc sach)) ky tang xa hoi. hieu ((va nam) or (va nay)) thuc va dan tai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) ky tang xa hoi. hieu ((va nam) OR (va nay)) thuc va dan tai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) ky tang xa hoi. hieu ((va nam) or (va nay)) thuc va dan tai cuu tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) ky tang xa hoi. hieu ((va nam) or (va nay)) thuc va dan tai cuu tre*.