Question: when did louisiana become a part of the united states
[{'answer': '20 December 1803'}, {'provenance': [{'wikipedia_id': '17628', 'title': 'Louisiana Purchase', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 752, 'bleu_score': 0.8008183576645541, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8085381580398138792}, 'section': 'Section::::Background.\n'}]}]