Question: when did the american flag become a symbol
[{'answer': 'April 1861', 'provenance': [{'wikipedia_id': '11447', 'title': 'Flag of the United States', 'start_paragraph_id': 42, 'start_character': 278, 'end_paragraph_id': 42, 'end_character': 288, 'bleu_score': 1.0, 'section': 'Section::::Symbolism.\n'}]}]