Question: who becomes chief of surgery in season 12
[{'answer': 'Miranda Bailey', 'provenance': [{'wikipedia_id': '46641890', 'title': "Grey's Anatomy (season 12)", 'start_paragraph_id': 6, 'start_character': 380, 'end_paragraph_id': 6, 'end_character': 394, 'bleu_score': 1.0, 'section': 'Section::::Plots.\n'}]}, {'provenance': [{'wikipedia_id': '46641890', 'title': "Grey's Anatomy (season 12)", 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 621, 'bleu_score': 0.9812185674664711, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15977254698119651353}, 'section': 'Section::::Plots.\n'}]}]