Perhaps you should try some spelling variations:
dong hoa » dong hoc, dong co
hieu van » hieu va, thien van, lieu va
van hanh » van thanh, ban hanh, van anh
cau tren » cu tren, dau tren, ca tren
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
van lam » van nam
hanh va » hang va, hanh vi
lam vo » lam co, lam so, lam vu
va cau » van cau, va cac, va dau

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: so sach ky ((dong hoa) OR (van xay)) hoi. hieu van lam vo van hanh va cau tren~.
• Adding a wildcard symbol may retrieve word variants: so sach ky ((dong hoa) or (van xay)) hoi. hieu van lam vo van hanh va cau tren*.