What is the producer of the television shows whose channel is CBBC?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/channel> <http://dbpedia.org/resource/CBBC_(TV_channel)> . ?x <http://dbpedia.org/ontology/producer> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/TelevisionShow>}
CBBC_(TV_channel)