Question: when did the us last host the summer olympics
[{'answer': '1996', 'provenance': [{'wikipedia_id': '2112059', 'title': 'United States at the Olympics', 'start_paragraph_id': 40, 'start_character': 73, 'end_paragraph_id': 40, 'end_character': 77, 'bleu_score': 1.0, 'section': 'Section::::Russia–United States rivalry.:Ice hockey.\n'}]}]