Question: when was the central bank of nigeria established
[{'answer': '1958', 'provenance': [{'wikipedia_id': '4930991', 'title': 'Central Bank of Nigeria', 'start_paragraph_id': 1, 'start_character': 123, 'end_paragraph_id': 1, 'end_character': 127, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4930991', 'title': 'Central Bank of Nigeria', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 168, 'bleu_score': 0.934334813046729, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12498327400599262334}, 'section': 'Section::::Abstract.'}]}]