Which politician's constituency is led by the SF Board of Supervisors?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/leaderTitle> <http://dbpedia.org/resource/San_Francisco_Board_of_Supervisors> . ?uri <http://dbpedia.org/property/constituency> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/OfficeHolder>}
San_Francisco_Board_of_Supervisors