Question: who sang background on you're so vain
[{'answer': 'Mick Jagger', 'provenance': [{'wikipedia_id': '609802', 'title': "You're So Vain", 'start_paragraph_id': 4, 'start_character': 104, 'end_paragraph_id': 4, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]