Where is the headquarters of the public transit system which owns the American Boulevard (Metro Transit station) located ?
SELECT DISTINCT ?uri WHERE { <http://dbpedia.org/resource/American_Boulevard_(Metro_Transit_station)> <http://dbpedia.org/ontology/owningOrganisation> ?x . ?x <http://dbpedia.org/property/headquarters> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/PublicTransitSystem>}
American_Boulevard_(Metro_Transit_station)