Question: when's the last time duke won a national championship
[{'answer': '2015', 'provenance': [{'wikipedia_id': '8219053', 'title': "Duke Blue Devils men's basketball", 'start_paragraph_id': 11, 'start_character': 111, 'end_paragraph_id': 11, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Team history.:Retired numbers.\n'}]}, {'provenance': [{'wikipedia_id': '8219053', 'title': "Duke Blue Devils men's basketball", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 1134, 'bleu_score': 0.697335471350874, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4060544991893638188}, 'section': 'Section::::Abstract.'}]}]