Question: when was the last time us hosted summer olympics
[{'answer': '1996', 'provenance': [{'wikipedia_id': '27566', 'title': 'Summer Olympic Games', 'start_paragraph_id': 3, 'start_character': 171, 'end_paragraph_id': 3, 'end_character': 175, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '27566', 'title': 'Summer Olympic Games', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 569, 'bleu_score': 0.7489126772133791, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3373330781094702488}, 'section': 'Section::::Abstract.'}]}]