Perhaps you should try some spelling variations:
huong doi » huong dan, dung doi
doc sach » hoc sach, toc sach, nuoc sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
cuu tre » cua tre, cau tren, cau treo
cac tu » cac thu, cach tu, tac tu

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 ky nang xa hoi. hieu va ((cac tu) or (cac du)) va ((huong doi) OR (trong doi)) cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky nang xa hoi. hieu va ((cac tu) OR (cac du)) va ((huong doi) OR (trong doi)) cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky nang xa hoi. hieu va ((cac tu) or (cac du)) va ((huong doi) OR (trong doi)) cuu tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky nang xa hoi. hieu va ((cac tu) or (cac du)) va ((huong doi) OR (trong doi)) cuu tre*.