Question: when did they change pennies from copper to zinc
[{'answer': '1943', 'provenance': [{'wikipedia_id': '164092', 'title': 'Penny (United States coin)', 'start_paragraph_id': 6, 'start_character': 3, 'end_paragraph_id': 6, 'end_character': 7, 'bleu_score': 1.0, 'section': 'Section::::History of composition.\n'}]}]