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

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) OR (lam so)) van hanh va cau tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ky ((dong hoa) or (van xay)) hoi. hieu van ((lam vo) OR (lam so)) 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) OR (lam so)) van hanh va cau tren*.