Question: who sang the theme song to fireball xl5
[{'answer': 'Don Spencer', 'provenance': [{'wikipedia_id': '1010129', 'title': 'Fireball XL5', 'start_paragraph_id': 17, 'start_character': 152, 'end_paragraph_id': 17, 'end_character': 163, 'bleu_score': 1.0, 'section': 'Section::::Theme song and merchandising.\n'}]}]