Question: where is the primary chemoreceptor for co2 located
[{'answer': 'medulla oblongata', 'provenance': [{'wikipedia_id': '489289', 'title': 'Chemoreceptor', 'start_paragraph_id': 26, 'start_character': 79, 'end_paragraph_id': 26, 'end_character': 96, 'bleu_score': 1.0, 'section': 'Section::::Physiology.:Control of breathing.\n'}]}, {'provenance': [{'wikipedia_id': '489289', 'title': 'Chemoreceptor', 'start_paragraph_id': 26, 'start_character': 0, 'end_paragraph_id': 26, 'end_character': 306, 'bleu_score': 0.8752376177722321, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16303752821242056786}, 'section': 'Section::::Physiology.:Control of breathing.\n'}]}]