Question: when did nigeria become a member of the united nations
[{'answer': '1960', 'provenance': [{'wikipedia_id': '42512141', 'title': 'Nigeria and the United Nations', 'start_paragraph_id': 1, 'start_character': 106, 'end_paragraph_id': 1, 'end_character': 110, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]