Question: In how many countries do the rivers start which end at the Caspian Sea?
SPARQL query: SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/Caspian_Sea> . ?x <http://dbpedia.org/ontology/sourceCountry> ?uri  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Country>}
Answer: There are [15] source countries of the rivers whose mouth is Caspian Sea.