Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thuc dan » thuc hanh, hoc dan
hai cuu » hai cua, hai chu, hai cuc
dau hai » dai hai, dau ha, cau hai
cuu tre » cua tre, cau tren, cau treo
hieu va » lieu va, hieu qua
dang xa » dang xay, lang xa, dang ha
ky dang » ky nang, ky danh
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 sinh)) ky dang xa hoi. hieu va nay ((thuc vat) or (thuc dan)) dau hai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc vat) OR (thuc dan)) dau hai cuu tre.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sinh)) ky dang xa hoi. hieu va nay ((thuc vat) or (thuc dan)) dau hai cuu tre*.