Question: when did big bend became a national park
[{'answer': 'June 12 , 1944', 'provenance': [{'wikipedia_id': '306829', 'title': 'Big Bend National Park', 'start_paragraph_id': 26, 'start_character': 525, 'end_paragraph_id': 26, 'end_character': 539, 'bleu_score': 1.0, 'section': 'Section::::Human history.\n'}]}]