Question: who was the only u.s. president whose grandfather was also president
[{'answer': 'Benjamin Harrison', 'provenance': [{'wikipedia_id': '7766419', 'title': 'Benjamin Harrison', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 17, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '7766419', 'title': 'Benjamin Harrison', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 880, 'bleu_score': 0.9342298169490251, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2387765721373113475}, 'section': 'Section::::Abstract.'}]}]