Question: who acted as the constitutional advisor to the constituent assembly
[{'answer': 'B.N. Rau', 'provenance': [{'wikipedia_id': '1589530', 'title': 'Constituent Assembly of India', 'start_paragraph_id': 18, 'start_character': 12, 'end_paragraph_id': 18, 'end_character': 18, 'bleu_score': 1.0, 'section': 'Section::::Organization.\n'}]}]