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
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
ba truc » cau truc, ba trung, dai truc
nang xa » nang x, lang xa, nang ma
ha truc » ha thuc, hang truc, cau truc
cuu tre » cua tre, cau tren, cau treo
y nang » ky nang, ly nang, v nang

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 y 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 y 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 y nang xa hoi. hieu van ((ha truc) or (ba truc)) va doan vi ((dua tren) or (cuu tre))*.