Question: when was the first successful heart transplant performed
[{'answer': 'December 3 , 1967'}, {'provenance': [{'wikipedia_id': '7015', 'title': 'Christiaan Barnard', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 778, 'bleu_score': 0.664570755063541, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10220043455649586491}, 'section': 'Section::::Abstract.'}]}]