Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thuc dan » thuc hanh, hoc dan, thuc vat
ky tang » ky dang, kho tang, ky trong
dan dan » dang dan, ban dan, dao dan
dan vai » dan va, dan tai, dan vat
vai cuu » vai cua
cuu tre » cua tre, cau tren, cau treo
va nam » van nam, ha nam
va nay » va ngay, va cay

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