which subsidiary of air china serves both shenzhen bao'an international airport and shenzhen bao'an international airport ?
select distinct var_uri where brack_open dbr_Air_China dbo_subsidiary var_uri sep_dot var_uri dbo_targetAirport dbr_Shenzhen_Bao'an_International_Airport sep_dot var_uri dbo_targetAirport dbr_Shenzhen_Bao'an_International_Airport sep_dot brack_close