Question: who sings the song big iron on his hip
[{'answer': 'Marty Robbins', 'provenance': [{'wikipedia_id': '29640848', 'title': 'Big Iron', 'start_paragraph_id': 1, 'start_character': 56, 'end_paragraph_id': 1, 'end_character': 69, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '29640848', 'title': 'Big Iron', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 351, 'bleu_score': 0.968982777549629, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4976768216265725426}, 'section': 'Section::::Abstract.'}]}]