Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cac treo » cac tro, cau treo, cac trieu
ky lang » ky dang, ky tang, tay lang
thuc va » thuc vat, thuc dan, thuc day
dao vai » dao van, dao va, dao bai
vai cac » va cac, tai cac, voi cac
va nam » ha nam, va nay
va dao » ca dao

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 ((ky lang) OR (ky nang)) xa hoi. hieu ((va nam) or (van nam)) thuc va dao vai cac treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky nang)) xa hoi. hieu ((va nam) OR (van nam)) thuc va dao vai cac treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) OR (ky nang)) xa hoi. hieu ((va nam) or (van nam)) thuc va dao vai cac treo".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) OR (ky nang)) xa hoi. hieu ((va nam) or (van nam)) thuc va dao vai cac treo*.