Question: where was the first heart transplant performed in the united states
[{'answer': 'University of Mississippi Medical Center', 'provenance': [{'wikipedia_id': '30876400', 'title': 'Heart transplantation', 'start_paragraph_id': 5, 'start_character': 64, 'end_paragraph_id': 5, 'end_character': 104, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '30876400', 'title': 'Heart transplantation', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 1094, 'bleu_score': 0.975009253695653, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2711149523248624159}, 'section': 'Section::::History.\n'}]}]