Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
thuc day » thuc dan, thuc vat
ky dang » ky nang, ky danh
dang xa » dang xay, lang xa, dang ha
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan
dau hai » dai hai, dau ha, cau hai
hai cuu » hai cua, hai chu, hai cuc
cuu tre » cua tre, cau tren, cau treo
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: ((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc va) OR (thuc day)) dau hai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc va) OR (thuc day)) dau hai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc va) OR (thuc day)) dau hai cuu tre".
• Adding a wildcard symbol may retrieve word variants: ((doc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc va) OR (thuc day)) dau hai cuu tre*.