Question: how many vice presidents of the united states have there been
[{'answer': '48', 'provenance': [{'wikipedia_id': '13150787', 'title': 'List of Vice Presidents of the United States', 'start_paragraph_id': 1, 'start_character': 16, 'end_paragraph_id': 1, 'end_character': 18, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '13150787', 'title': 'List of Vice Presidents of the United States', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 587, 'bleu_score': 0.925902437792197, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 895316605162997904}, 'section': 'Section::::Abstract.'}]}]