Question: when was abuja became the capital of nigeria
[{'answer': '12 December 1991', 'provenance': [{'wikipedia_id': '56823', 'title': 'Abuja', 'start_paragraph_id': 1, 'start_character': 247, 'end_paragraph_id': 1, 'end_character': 263, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '56823', 'title': 'Abuja', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 532, 'bleu_score': 0.8595255862489851, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13742517537168536706}, 'section': 'Section::::Abstract.'}]}]