Question: what was west africa’s earliest known culture
[{'answer': 'Nok culture', 'provenance': [{'wikipedia_id': '2435657', 'title': 'History of West Africa', 'start_paragraph_id': 2, 'start_character': 605, 'end_paragraph_id': 2, 'end_character': 616, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2435657', 'title': 'History of West Africa', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 1303, 'bleu_score': 0.7199515435717321, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6368480478729029493}, 'section': 'Section::::Abstract.'}]}]