Question: when was the last time the us detonated a nuclear weapon
[{'answer': '23 September 1992', 'provenance': [{'wikipedia_id': '2032576', 'title': 'Nuclear weapons of the United States', 'start_paragraph_id': 23, 'start_character': 25, 'end_paragraph_id': 23, 'end_character': 42, 'bleu_score': 1.0, 'section': 'Section::::Nuclear weapons testing.\n'}]}]