which subsidiary of air china serves both shenyang taoxian international airport and guangzhou baiyun international airport ?
select distinct var_uri where brack_open dbr_Air_China dbo_subsidiary var_uri sep_dot var_uri dbo_targetAirport dbr_Shenyang_Taoxian_International_Airport sep_dot var_uri dbo_targetAirport dbr_Guangzhou_Baiyun_International_Airport sep_dot brack_close