Question: who sings backup vocals on gimme shelter
[{'answer': 'Merry Clayton', 'provenance': [{'wikipedia_id': '6503391', 'title': 'Merry Clayton', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6503391', 'title': 'Merry Clayton', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 503, 'bleu_score': 0.976043556018343, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4818430921664822598}, 'section': 'Section::::Abstract.'}]}]