Question: when was the mississippi river levee system built
[{'answer': '1928', 'provenance': [{'wikipedia_id': '301810', 'title': 'Great Mississippi Flood of 1927', 'start_paragraph_id': 16, 'start_character': 144, 'end_paragraph_id': 16, 'end_character': 148, 'bleu_score': 1.0, 'section': 'Section::::Political and social responses.\n'}]}, {'provenance': [{'wikipedia_id': '301810', 'title': 'Great Mississippi Flood of 1927', 'start_paragraph_id': 16, 'start_character': 0, 'end_paragraph_id': 16, 'end_character': 652, 'bleu_score': 0.9806740509884301, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15208083864137760601}, 'section': 'Section::::Political and social responses.\n'}]}]