Who are the writers of the singles whose music genre is Rhythm and blues ?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/genre> <http://dbpedia.org/resource/Rhythm_and_blues> . ?x <http://dbpedia.org/ontology/writer> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Single>}
Rhythm_and_blues