Question: when was the last time pistons won a championship
[{'answer': '2004', 'provenance': [{'wikipedia_id': '72871', 'title': 'Detroit Pistons', 'start_paragraph_id': 1, 'start_character': 747, 'end_paragraph_id': 1, 'end_character': 751, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '72871', 'title': 'Detroit Pistons', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 751, 'bleu_score': 0.8860343004328001, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3428022283374930377}, 'section': 'Section::::Abstract.'}]}]