Question: who wrote back to the future theme song
[{'answer': 'Alan Silvestri', 'provenance': [{'wikipedia_id': '10451921', 'title': 'Back to the Future (soundtrack)', 'start_paragraph_id': 1, 'start_character': 205, 'end_paragraph_id': 1, 'end_character': 219, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '10451921', 'title': 'Back to the Future (soundtrack)', 'start_paragraph_id': 30, 'start_character': 0, 'end_paragraph_id': 30, 'end_character': 942, 'bleu_score': 0.9448584603671871, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11476873438426320308}, 'section': 'Section::::Miscellaneous.\n'}]}]