What is {stable versions} of {operating system} of {Skype} ?
What stable versions of Skype's operating system?
Which   stable versions of operating system of Skype ?
SELECT ?q WHERE { ?v property:software_version_identifier ?q . resource:Skype property:operating_system ?v }
SELECT ?answer WHERE { ?statement1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q40984> . ?statement1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P306>. ?statement1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?X . ?statement2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?X. ?statement2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P348> . ?statement2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?answer . }
SELECT ?answer WHERE { wd:Q40984 wdt:P306 ?X . ?X wdt:P348 ?answer}