machine_question: what were adolf hitler 's parents names and that died on 1907-12-21
question: Which parent of Adolf Hitler died on 12-21-1907?
sparql: PREFIX ns: <http://rdf.freebase.com/ns/>
  SELECT DISTINCT ?x
  WHERE {
  FILTER (?x != ns:m.07_m9_)
  FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
  ns:m.07_m9_ ns:people.person.parents ?x .
  ?x ns:people.deceased_person.date_of_death "1907-12-21"^^xsd:dateTime . 
  }
webqsp_question: what were adolf hitler 's parents names