Question: when was the last time university of michigan 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.'}]}, {'provenance': [{'wikipedia_id': '6142330', 'title': 'Michigan Wolverines football', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11306199294027071223}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6142330', 'title': 'Michigan Wolverines football', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 456, 'bleu_score': 0.9754554449993441, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11306199294027071223}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6142330', 'title': 'Michigan Wolverines football', 'section': 'Section::::Abstract.', 'start_paragraph_id': 2, 'end_paragraph_id': 2, 'meta': {'evidence_span': ['1997', 'The Wolverines claim 11 national championships, most recently that of the 1997 squad voted atop the final AP Poll.', 'The Wolverines claim 11 national championships, most recently that of the 1997 squad voted atop the final AP Poll']}}]}]