Question: who had the longest tenure as president of the usa
[{'answer': 'Franklin D. Roosevelt', 'provenance': [{'wikipedia_id': '1038417', 'title': 'List of Presidents of the United States by time in office', 'start_paragraph_id': 2, 'start_character': 340, 'end_paragraph_id': 2, 'end_character': 361, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]