Question: WHat is the capital of the country which inludes the Duisburg airport?
Answer(s):
answer: Berlin

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:location.location.contains ?k .
?k ns:aviation.airport.serves ns:m.0ps1q . 
?c ns:location.country.capital ?x .
}