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