Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
thuc day » thuc vat
thuc dan » thuc hanh, hoc dan, thuc vat
tay lang » tai lang, tay tang, tay quang
hieu va » lieu va, hieu qua
ky dang » ky nang, ky danh
dan vai » dan va, dan tai, dan vat
vai cuu » vai cua
cuu tre » cua tre, cau tren, cau treo
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: doc sach ((tay lang) or (ky dang)) xa hoi. hieu va nam ((thuc dan) or (thuc day)) dan vai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((tay lang) OR (ky dang)) xa hoi. hieu va nam ((thuc dan) OR (thuc day)) dan vai cuu tre.
• Adding a wildcard symbol may retrieve word variants: doc sach ((tay lang) or (ky dang)) xa hoi. hieu va nam ((thuc dan) or (thuc day)) dan vai cuu tre*.