Question: Where does the rivers ending in lake washington begin?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/Lake_Washington> . ?x <http://dbpedia.org/property/sourceLocation> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}