Question: when was mandalay bay hotel in las vegas built
[{'answer': 'March 2 , 1999 ;', 'provenance': [{'wikipedia_id': '724760', 'title': 'Mandalay Bay', 'start_paragraph_id': 6, 'start_character': 18, 'end_paragraph_id': 6, 'end_character': 34, 'bleu_score': 0.668740304976422, 'section': 'Section::::History.\n'}]}]