Question: who is the current us supreme court chief justice
[{'answer': 'John Roberts', 'provenance': [{'wikipedia_id': '31739', 'title': 'Chief Justice of the United States', 'start_paragraph_id': 4, 'start_character': 155, 'end_paragraph_id': 4, 'end_character': 167, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '31739', 'title': 'Chief Justice of the United States', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 343, 'bleu_score': 0.530582438670381, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1725263337516822537}, 'section': 'Section::::Abstract.'}]}]