Question: What was the book that lead to Sagan's Cosmos, about?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/subsequentWork> <http://dbpedia.org/resource/Cosmos_(Carl_Sagan_book)> . ?x <http://dbpedia.org/property/subject> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Book>}