How many people have been presenters for NBC shows?
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/channel> <http://dbpedia.org/resource/NBC> . ?x <http://dbpedia.org/property/presenter> ?uri  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Person>}
NBC