Question: who sang ol man river in showboat 1951
[{'answer': 'Warfield', 'provenance': [{'wikipedia_id': '900050', 'title': 'William Warfield', 'start_paragraph_id': 0, 'start_character': 8, 'end_paragraph_id': 0, 'end_character': 16, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '900050', 'title': 'William Warfield', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 1116, 'bleu_score': 0.970452755483536, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13335862862913498791}, 'section': 'Section::::Biography.:Early life and career.\n'}]}]