Question: what is the muscular layer of a blood vessel
[{'answer': 'Tunica intima', 'provenance': [{'wikipedia_id': '48530', 'title': 'Blood vessel', 'start_paragraph_id': 6, 'start_character': 30, 'end_paragraph_id': 6, 'end_character': 43, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}, {'answer': 'Tunica media', 'provenance': [{'wikipedia_id': '48530', 'title': 'Blood vessel', 'start_paragraph_id': 7, 'start_character': 30, 'end_paragraph_id': 7, 'end_character': 42, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}, {'answer': 'Tunica adventitia', 'provenance': [{'wikipedia_id': '48530', 'title': 'Blood vessel', 'start_paragraph_id': 8, 'start_character': 36, 'end_paragraph_id': 8, 'end_character': 53, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}]