Question: Which country has outflow of  Lake Uniamsi and  inflows of the Cahora Bassa?
SPARQL:
SELECT DISTINCT ?uri WHERE { <http://dbpedia.org/resource/Lake_Uniamési> <http://dbpedia.org/property/outflow> ?uri. <http://dbpedia.org/resource/Cahora_Bassa> <http://dbpedia.org/property/inflow> ?uri}