Question: Which river ends at  Thames Estuary and North Sea?
SPARQL query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?uri WHERE { ?uri onto:riverMouth <http://dbpedia.org/resource/Thames_Estuary> . ?uri onto:riverMouth <http://dbpedia.org/resource/North_Sea> . ?uri rdf:type onto:River}