Question: who played the joker in the dark knoght
[{'answer': 'Australian actor Heath Ledger', 'provenance': [{'wikipedia_id': '21145395', 'title': 'Joker (The Dark Knight)', 'start_paragraph_id': 1, 'start_character': 196, 'end_paragraph_id': 1, 'end_character': 225, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '21145395', 'title': 'Joker (The Dark Knight)', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 775, 'bleu_score': 0.7110673458240411, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4895088973924734460}, 'section': 'Section::::Abstract.'}]}]