Perhaps you should try some spelling variations:
dua tren » dung tren
vu sach » vu bach, su sach, vu khach
dung co » dung cho, dung cong, dung cua
va dung » van dung, va duong, vat dung
sach ky » sac ky, sach y, sach ty
cao tuc » dao tuc, cao duc, cao suc
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
nang xa » nang x, nang ma, mang xa
cuu tre » cua tre, cau tren, cau treo
va cao » va cac, va co, va dao
tuc va » thuc va, truc va, tuc xa

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

• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ky ((nang xa) OR (lang xa)) hoi. hieu va cao tuc va dung co ((dua tren) OR (cuu tre))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach ky ((nang xa) OR (lang xa)) hoi. hieu va cao tuc va dung co ((dua tren) or (cuu tre))~".
• Adding a wildcard symbol may retrieve word variants: vu sach ky ((nang xa) OR (lang xa)) hoi. hieu va cao tuc va dung co ((dua tren) or (cuu tre))*.