Question: What is the alma mater of the scientists  known for  String theory?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/knownFor> <http://dbpedia.org/resource/String_theory> . ?x <http://dbpedia.org/property/almaMater> ?uri . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Scientist>}