Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
dau tren » dau tien, dat tren, dau tieng
hoc sach » hoc sinh, hoc cac, hoc anh
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau
dan va » doan va, dan ca, ban va
va am » va lam, va cam

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 lang xa hoi. hieu va am thuc va dan va ((dau tren) or (cua tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky lang xa hoi. hieu va am thuc va dan va ((dau tren) OR (cua tre)).
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky lang xa hoi. hieu va am thuc va dan va ((dau tren) or (cua tre))*.