Question: when did christmas become an official us holiday
[{'answer': 'June 28 , 1870', 'provenance': [{'wikipedia_id': '6237', 'title': 'Christmas', 'start_paragraph_id': 68, 'start_character': 412, 'end_paragraph_id': 68, 'end_character': 426, 'bleu_score': 1.0, 'section': 'Section::::History.:Modern history.:19th century.\n'}]}, {'provenance': [{'wikipedia_id': '6237', 'title': 'Christmas', 'start_paragraph_id': 68, 'start_character': 0, 'end_paragraph_id': 68, 'end_character': 490, 'bleu_score': 0.9735040436119741, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5239422913695441347}, 'section': 'Section::::History.:Modern history.:19th century.\n'}]}]