Question: how long did gunsmoke stay on the air
[{'answer': 'for 20 seasons', 'provenance': [{'wikipedia_id': '174220', 'title': 'Gunsmoke', 'start_paragraph_id': 2, 'start_character': 201, 'end_paragraph_id': 2, 'end_character': 215, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '174220', 'title': 'Gunsmoke', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 618, 'bleu_score': 0.9813933169956551, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10399550942670004393}, 'section': 'Section::::Abstract.'}]}]