Question: when does meredith become chief of general surgery
[{'answer': '2015', 'provenance': [{'wikipedia_id': '7687013', 'title': 'Meredith Grey', 'start_paragraph_id': 1, 'start_character': 604, 'end_paragraph_id': 1, 'end_character': 608, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '7687013', 'title': 'Meredith Grey', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 939, 'bleu_score': 0.9238539794125641, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8709403485305014810}, 'section': 'Section::::Abstract.'}]}]