Question: when did the gold standard end in the us
[{'answer': 'August 15 , 1971', 'provenance': [{'wikipedia_id': '37412', 'title': 'Gold standard', 'start_paragraph_id': 65, 'start_character': 446, 'end_paragraph_id': 65, 'end_character': 463, 'bleu_score': 1.0, 'section': 'Section::::Abandonment of the gold standard.:Bretton Woods.\n'}]}, {'provenance': [{'wikipedia_id': '37412', 'title': 'Gold standard', 'start_paragraph_id': 65, 'start_character': 0, 'end_paragraph_id': 65, 'end_character': 479, 'bleu_score': 0.9257921357402691, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9872186862664450465}, 'section': 'Section::::Abandonment of the gold standard.:Bretton Woods.\n'}]}]