Question: where is oxygen attached on a hemoglobin molecule
[{'answer': 'The iron ion', 'provenance': [{'wikipedia_id': '13483', 'title': 'Hemoglobin', 'start_paragraph_id': 25, 'start_character': 250, 'end_paragraph_id': 25, 'end_character': 262, 'bleu_score': 1.0, 'section': 'Section::::Structure.\n'}]}, {'provenance': [{'wikipedia_id': '13483', 'title': 'Hemoglobin', 'start_paragraph_id': 25, 'start_character': 0, 'end_paragraph_id': 25, 'end_character': 932, 'bleu_score': 0.9876155018005031, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17208616768764947626}, 'section': 'Section::::Structure.\n'}]}]