Question: who played dr brown in back to the future
[{'answer': 'Christopher Allen Lloyd', 'provenance': [{'wikipedia_id': '256406', 'title': 'Christopher Lloyd', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 23, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]