Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau tren » cu tren, dau tren, ca tren
hoc sach » hoc sinh, hoc cac, hoc anh
dau vai » dau va, dau hai, dau tai
thuc va » thuc vat, thuc dan, thuc day
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
dang xa » dang xay, lang xa, dang ha
ky dang » ky nang, ky danh
va dau » va dao
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 dau vai ((cau tren) or (cua 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 dau vai ((cau tren) OR (cua tre)).
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky dang xa hoi. hieu va nam thuc va dau vai ((cau tren) or (cua tre))*.