Question: when did the first human heart transplant happen
[{'answer': '3 December 1967', 'provenance': [{'wikipedia_id': '7015', 'title': 'Christiaan Barnard', 'start_paragraph_id': 1, 'start_character': 235, 'end_paragraph_id': 1, 'end_character': 250, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '7015', 'title': 'Christiaan Barnard', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 778, 'bleu_score': 0.70615581516406, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15137384661849744282}, 'section': 'Section::::Abstract.'}]}]