Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
nam thuc » nam thuoc, am thuc, nam thu
dan vai » dan tai, dan vat, den vai
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
cuu tre » cua tre, cau tren, cau treo
dang xa » dang xay, lang xa, dang ha
ky dang » ky nang, ky danh
dan va » doan va, dan ca, ban va
va nam » van nam, ha nam, va nay

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