Question: when did they stop using silver in us coins
[{'answer': 'July 23 , 1965', 'provenance': [{'wikipedia_id': '10566622', 'title': 'Coinage Act of 1965', 'start_paragraph_id': 28, 'start_character': 619, 'end_paragraph_id': 28, 'end_character': 633, 'bleu_score': 1.0, 'section': 'Section::::Legislation.\n'}]}, {'answer': '1970', 'provenance': [{'wikipedia_id': '10566622', 'title': 'Coinage Act of 1965', 'start_paragraph_id': 1, 'start_character': 272, 'end_paragraph_id': 1, 'end_character': 276, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '10566622', 'title': 'Coinage Act of 1965', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 280, 'bleu_score': 0.768359992294883, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11372971679788492454}, 'section': 'Section::::Abstract.'}]}]