Question: when did the nfl start playing on christmas day
[{'answer': '1971', 'provenance': [{'wikipedia_id': '15541402', 'title': 'National Football League Christmas games', 'start_paragraph_id': 2, 'start_character': 65, 'end_paragraph_id': 2, 'end_character': 69, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '15541402', 'title': 'National Football League Christmas games', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 345, 'bleu_score': 0.9694566079002921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5578755140965132135}, 'section': 'Section::::Abstract.'}]}]