Question: who is the audience of letter from birmingham jail
[{'answer': 'an open letter', 'provenance': [{'wikipedia_id': '356391', 'title': 'Letter from Birmingham Jail', 'start_paragraph_id': 1, 'start_character': 118, 'end_paragraph_id': 1, 'end_character': 132, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '356391', 'title': 'Letter from Birmingham Jail', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 545, 'bleu_score': 0.978138775770484, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1783499315521498647}, 'section': 'Section::::Abstract.'}]}]