Name the military unit whose garrison is Arlington County, Virginia and command structure is United States Department of Defense?
SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/garrison> <http://dbpedia.org/resource/Arlington_County,_Virginia> . ?uri <http://dbpedia.org/ontology/commandStructure> <http://dbpedia.org/resource/United_States_Department_of_Defense>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/MilitaryUnit>}
Arlington_County,_Virginia United_States_Department_of_Defense