Question: what type of muscle tissue is found in the iris
[{'answer': 'a sphincter muscle', 'provenance': [{'wikipedia_id': '86801', 'title': 'Iris (anatomy)', 'start_paragraph_id': 4, 'start_character': 23, 'end_paragraph_id': 4, 'end_character': 41, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}, {'answer': 'a set of dilator muscles', 'provenance': [{'wikipedia_id': '86801', 'title': 'Iris (anatomy)', 'start_paragraph_id': 4, 'start_character': 116, 'end_paragraph_id': 4, 'end_character': 140, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}, {'provenance': [{'wikipedia_id': '86801', 'title': 'Iris (anatomy)', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 896, 'bleu_score': 0.7921998630686221, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13518467777828051896}, 'section': 'Section::::Structure.\n'}]}]