Question: when did the us go off the silver standard
[{'answer': '1873', 'provenance': [{'wikipedia_id': '2235798', 'title': 'Silver standard', 'start_paragraph_id': 2, 'start_character': 979, 'end_paragraph_id': 2, 'end_character': 983, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2235798', 'title': 'Silver standard', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 1401, 'bleu_score': 0.9916838112046971, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15755149848140759940}, 'section': 'Section::::Abstract.'}]}]