Question: who played mandela in long walk to freedom
[{'answer': 'Idris Elba', 'provenance': [{'wikipedia_id': '38866589', 'title': 'Mandela: Long Walk to Freedom', 'start_paragraph_id': 1, 'start_character': 164, 'end_paragraph_id': 1, 'end_character': 174, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]