Rivers from which countries flow into the Caspian?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/Caspian_Sea> . ?x <http://dbpedia.org/ontology/sourceCountry> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}
Caspian_Sea