Perhaps you should try some spelling variations:
dua tren » dung tren
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
ba truc » cau truc, ba trung, dai truc
ha truc » ha thuc, hang truc, cau truc
nang xa » nang x, lang xa, nang ma
cuu tre » cua tre, cau tren, cau treo

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ky nang xa hoi. hieu van ((ha truc) OR (ba truc)) va doan vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang xa hoi. hieu van ((ha truc) OR (ba truc)) va doan vi ((dua tren) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang xa hoi. hieu van ((ha truc) OR (ba truc)) va doan vi ((dua tren) or (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang xa hoi. hieu van ((ha truc) OR (ba truc)) va doan vi ((dua tren) or (cuu tre))*.