List the birth city of the politicians of Democratic Party.
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/party> <http://dbpedia.org/resource/Democratic_Party_(United_States)> . ?x <http://dbpedia.org/ontology/birthPlace> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Politician>}
Democratic_Party_(United_States)