Question: who played the title role in the 2008 film the duchess
[{'answer': 'Keira Knightley', 'provenance': [{'wikipedia_id': '12507175', 'title': 'The Duchess (film)', 'start_paragraph_id': 29, 'start_character': 23, 'end_paragraph_id': 29, 'end_character': 38, 'bleu_score': 1.0, 'section': 'Section::::Production.\n'}]}, {'provenance': [{'wikipedia_id': '12507175', 'title': 'The Duchess (film)', 'start_paragraph_id': 12, 'start_character': 0, 'end_paragraph_id': 12, 'end_character': 73, 'bleu_score': 0.7598356856515921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3642829617224916110}, 'section': 'Section::::Main cast.\n'}]}]