Question: what doubled the size of the united states in 1803
[{'answer': 'The Louisiana Purchase', 'provenance': [{'wikipedia_id': '17628', 'title': 'Louisiana Purchase', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]