Question: who all play for of the american football players at  Quarterback position?
SPARQL query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX prop: <http://dbpedia.org/property/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?uri WHERE { ?x prop:position <http://dbpedia.org/resource/Quarterback> . ?x onto:team ?uri  . ?x rdf:type onto:AmericanFootballPlayer}