Question: when did dc give land back to virginia
[{'answer': '1846', 'provenance': [{'wikipedia_id': '1809825', 'title': 'District of Columbia retrocession', 'start_paragraph_id': 2, 'start_character': 560, 'end_paragraph_id': 2, 'end_character': 564, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]