how many airlines have a hub at an airport run by aeroporto guglielmo marconi di bologna ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open var_x dbo_operator dbr_Aeroporto_Guglielmo_Marconi_di_Bologna_ attr_open company attr_close sep_dot var_uri dbo_hubAirport var_x sep_dot var_uri a dbo_Airline brack_close