Question: who sang mr sandman in back to the future
[{'answer': 'The Four Aces', 'provenance': [{'wikipedia_id': '10451921', 'title': 'Back to the Future (soundtrack)', 'start_paragraph_id': 17, 'start_character': 41, 'end_paragraph_id': 17, 'end_character': 54, 'bleu_score': 1.0, 'section': 'Section::::Track listing.\n'}]}]