Question: who became the chairman of tata sons in 2017
[{'answer': 'Natarajan Chandrasekaran', 'provenance': [{'wikipedia_id': '9221446', 'title': 'Tata Sons', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 24, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '9221446', 'title': 'Tata Sons', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 79, 'bleu_score': 0.850733133512352, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14255846539540904311}, 'section': 'Section::::Abstract.'}]}]