Question: who is current chief justice of supreme court
[{'answer': 'John Glover Roberts Jr.', 'provenance': [{'wikipedia_id': '1928850', 'title': 'John Roberts', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 23, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]