Question: who wrote the song a mighty fortress is our god
[{'answer': 'Martin Luther', 'provenance': [{'wikipedia_id': '449304', 'title': 'A Mighty Fortress Is Our God', 'start_paragraph_id': 1, 'start_character': 120, 'end_paragraph_id': 1, 'end_character': 133, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]