Question: is the vena cava a vein or artery
[{'answer': 'vein', 'provenance': [{'wikipedia_id': '242146', 'title': 'Inferior vena cava', 'start_paragraph_id': 1, 'start_character': 43, 'end_paragraph_id': 1, 'end_character': 47, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '242146', 'title': 'Inferior vena cava', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 358, 'bleu_score': 0.803288661994295, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3249213590523326548}, 'section': 'Section::::Abstract.'}]}]