Question: who plays the voice of optimus prime in transformers age of extinction
[{'answer': 'Cullen', 'provenance': [{'wikipedia_id': '810826', 'title': 'Peter Cullen', 'start_paragraph_id': 0, 'start_character': 6, 'end_paragraph_id': 0, 'end_character': 12, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]