Question: when did they stop making solid copper pennies
[{'answer': '1857', 'provenance': [{'wikipedia_id': '164092', 'title': 'Penny (United States coin)', 'start_paragraph_id': 12, 'start_character': 86, 'end_paragraph_id': 12, 'end_character': 90, 'bleu_score': 1.0, 'section': 'Section::::Designs.\n'}]}]