which subsidiary of air china serves both qingdao liuting international airport and qingdao liuting international airport ?
select distinct var_uri where brack_open dbr_Air_China dbo_subsidiary var_uri sep_dot var_uri dbo_targetAirport dbr_Qingdao_Liuting_International_Airport sep_dot var_uri dbo_targetAirport dbr_Qingdao_Liuting_International_Airport sep_dot brack_close