Question: when was the stratosphere hotel built in las vegas
[{'answer': '1996', 'provenance': [{'wikipedia_id': '693711', 'title': 'Stratosphere Las Vegas', 'start_paragraph_id': 18, 'start_character': 556, 'end_paragraph_id': 18, 'end_character': 560, 'bleu_score': 1.0, 'section': 'Section::::History.:Construction.\n'}]}]