Question: who wrote the poem o captain my captain
[{'answer': 'Walt Whitman', 'provenance': [{'wikipedia_id': '2601554', 'title': 'O Captain! My Captain!', 'start_paragraph_id': 1, 'start_character': 73, 'end_paragraph_id': 1, 'end_character': 85, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2601554', 'title': 'O Captain! My Captain!', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 506, 'bleu_score': 0.891390203442, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15856606562023526106}, 'section': 'Section::::Abstract.'}]}]