Question: In which UK city are the headquarters of the MI6?
SPARQL:
PREFIX res: <http://dbpedia.org/resource/>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT DISTINCT ?uri ?string WHERE 
{
	res:Secret_Intelligence_Service dbo:headquarter ?uri .
        ?uri dbo:country res:United_Kingdom .
	OPTIONAL { ?uri rdfs:label ?string. FILTER (lang(?string) = 'en') }
}