Question: who wrote the ballad of the green beret
[{'answer': 'Robin Moore', 'provenance': [{'wikipedia_id': '4760', 'title': 'Ballad of the Green Berets', 'start_paragraph_id': 2, 'start_character': 126, 'end_paragraph_id': 2, 'end_character': 137, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Staff Sgt . Barry Sadler', 'provenance': [{'wikipedia_id': '4760', 'title': 'Ballad of the Green Berets', 'start_paragraph_id': 2, 'start_character': 29, 'end_paragraph_id': 2, 'end_character': 53, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]