Question: when was the last time michigan football won a national championship
[{'answer': '1997', 'provenance': [{'wikipedia_id': '6142330', 'title': 'Michigan Wolverines football', 'start_paragraph_id': 2, 'start_character': 417, 'end_paragraph_id': 2, 'end_character': 421, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]