Perhaps you should try some spelling variations:
dua tren » dung tren
hieu van » hieu va, thien van, lieu va
vu sach » vu bach, su sach, vu khach
sach ty » sach y, sach tu, sach thu
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
ha thuy » thi thuy, thu thuy
ty nang » ky nang, ty xang, ty hang
cuu tre » cua tre, cau tren, cau treo
x hoi » xa hoi, o hoi, x ho

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach ty nang x hoi. hieu van ((cau truc) or (ha thuy)) va doan vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ty nang x hoi. hieu van ((cau truc) OR (ha thuy)) va doan vi ((dua tren) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: vu sach ty nang x hoi. hieu van ((cau truc) or (ha thuy)) va doan vi ((dua tren) or (cuu tre))*.