Question: who was the cheyenne leader whose village was attacked by american soldiers at sand creek
[{'answer': 'Black Kettle', 'provenance': [{'wikipedia_id': '209878', 'title': 'Sand Creek massacre', 'start_paragraph_id': 5, 'start_character': 251, 'end_paragraph_id': 5, 'end_character': 263, 'bleu_score': 1.0, 'section': 'Section::::Background.\n'}]}]