Question: when did season 4 of supernatural come out
[{'answer': 'September 18 , 2008', 'provenance': [{'wikipedia_id': '19396259', 'title': 'Supernatural (season 4)', 'start_paragraph_id': 1, 'start_character': 114, 'end_paragraph_id': 1, 'end_character': 133, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '19396259', 'title': 'Supernatural (season 4)', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 174, 'bleu_score': 0.8114217758899, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2921630268510301023}, 'section': 'Section::::Abstract.'}]}]