Question: when was the first open heart bypass surgery performed
[{'answer': '25 February 1960', 'provenance': [{'wikipedia_id': '804779', 'title': 'Cardiac surgery', 'start_paragraph_id': 16, 'start_character': 111, 'end_paragraph_id': 16, 'end_character': 127, 'bleu_score': 1.0, 'section': 'Section::::Types of cardiac surgery.:Open-heart surgery.\n'}]}, {'provenance': [{'wikipedia_id': '804779', 'title': 'Cardiac surgery', 'start_paragraph_id': 16, 'start_character': 0, 'end_paragraph_id': 16, 'end_character': 367, 'bleu_score': 0.9084940438173671, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10705741443804481249}, 'section': 'Section::::Types of cardiac surgery.:Open-heart surgery.\n'}]}]