Question: when did they stop making all silver half dollars
[{'answer': '1970', 'provenance': [{'wikipedia_id': '374699', 'title': 'Half dollar (United States coin)', 'start_paragraph_id': 5, 'start_character': 417, 'end_paragraph_id': 5, 'end_character': 421, 'bleu_score': 1.0, 'section': 'Section::::Circulation.\n'}]}, {'provenance': [{'wikipedia_id': '374699', 'title': 'Half dollar (United States coin)', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 421, 'bleu_score': 0.7987262848608131, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8762959774755946550}, 'section': 'Section::::Circulation.\n'}]}]