Question: how many police officers are killed in the line of duty each year
[{'answer': 'an average of 64'}, {'provenance': [{'wikipedia_id': '35981509', 'title': 'List of law enforcement officers killed in the line of duty in the United States', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 246, 'bleu_score': 0.8126992285623371, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11720072189259085560}, 'section': 'Section::::Overview by year.\n'}]}]