This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Poisoning, Subject name: Anatomy
[{'content': 'For blood and urine, preservative used is \nSelect and explain. \nA. Sodium chloride, B. Sodium fluoride, C. Sodium acetate, D. Sodium gluconate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: For blood, CSF, vitreous humor and urine, sodium fluoride is the preservative (100mg/10ml) Ref: FORENSIC MEDICINE AND TOXICOLOGY Dr PC IGNATIUS THIRD EDITION PAGE 404', 'role': 'assistant'}]