Question: who is often considered america's most prolific composer
[{'answer': 'Stephen Collins Foster', 'provenance': [{'wikipedia_id': '176594', 'title': 'Stephen Foster', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '176594', 'title': 'Stephen Foster', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 895, 'bleu_score': 0.769192120882593, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16354927170901386858}, 'section': 'Section::::Abstract.'}]}]