Question: what is a role of the pacemaker or sinoatrial node (san)
[{'answer': "heart 's natural pacemaker", 'provenance': [{'wikipedia_id': '598570', 'title': 'Sinoatrial node', 'start_paragraph_id': 1, 'start_character': 498, 'end_paragraph_id': 1, 'end_character': 524, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '598570', 'title': 'Sinoatrial node', 'start_paragraph_id': 1, 'start_character': 4, 'end_paragraph_id': 1, 'end_character': 634, 'bleu_score': 0.9430292469086691, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7988643105903095501}, 'section': 'Section::::Abstract.'}]}]