Question: what was the last nfl team to go undefeated
[{'answer': '1972 Miami Dolphins', 'provenance': [{'wikipedia_id': '2356756', 'title': 'Perfect season', 'start_paragraph_id': 3, 'start_character': 94, 'end_paragraph_id': 3, 'end_character': 113, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]