Question: when was the plaza hotel in las vegas built
[{'answer': 'July 2 , 1971', 'provenance': [{'wikipedia_id': '3302242', 'title': 'Plaza Hotel & Casino', 'start_paragraph_id': 7, 'start_character': 10, 'end_paragraph_id': 7, 'end_character': 27, 'bleu_score': 1.0, 'section': 'Section::::History.:Union Plaza Hotel and Casino.\n'}]}]