Question: when did the united states go on the gold standard
[{'answer': '1873', 'provenance': [{'wikipedia_id': '37412', 'title': 'Gold standard', 'start_paragraph_id': 11, 'start_character': 289, 'end_paragraph_id': 11, 'end_character': 293, 'bleu_score': 1.0, 'section': 'Section::::History.:Origins.\n'}]}, {'provenance': [{'wikipedia_id': '37412', 'title': 'Gold standard', 'start_paragraph_id': 11, 'start_character': 0, 'end_paragraph_id': 11, 'end_character': 495, 'bleu_score': 0.947703439108541, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10646208495438059253}, 'section': 'Section::::History.:Origins.\n'}]}]