Question: who has held a ufc title the longest
[{'answer': 'Anderson Silva', 'provenance': [{'wikipedia_id': '2430098', 'title': 'List of UFC champions', 'start_paragraph_id': 17, 'start_character': 113, 'end_paragraph_id': 17, 'end_character': 127, 'bleu_score': 1.0, 'section': "Section::::Men's championship history.:Middleweight Championship.\n"}]}]