What is the parent company of the airline whose hub is in Detroit?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/hubs> <http://dbpedia.org/resource/Detroit> . ?x <http://dbpedia.org/ontology/parentCompany> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Airline>}
Detroit