Question: where is the head office of the organization with headquarters  located in the city 8 Canada Square?
Answer(s):
answer: 8 Canada Square
answer: London

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ?c)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
?c ns:organization.organization.headquarters ?k .
?k ns:location.mailing_address.citytown ns:m.01sfbj . 
?c ns:organization.organization.headquarters ?y .
?y ns:location.mailing_address.citytown ?x .
}