Question: who has held the office of cm for longest period
[{'answer': 'Jyoti Basu', 'provenance': [{'wikipedia_id': '1509671', 'title': 'Pawan Kumar Chamling', 'start_paragraph_id': 7, 'start_character': 53, 'end_paragraph_id': 7, 'end_character': 63, 'bleu_score': 1.0, 'section': 'Section::::Political career.\n'}]}]