This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Forensic Medicine
[{'content': 'While dispatching blood and urine for chemical analysis, sodium fluoride is added as preservative in the following concentration - \nSelect and explain. \nA. 30 mg/10 ml, B. 40 mg/10 ml, C. 50 mg/ ml, D. 100 mg/10 ml', 'role': 'user'}, {'content': 'Answer: D \nExplanation: 10 mg/ml of Na-fluride (i.e. 100 mg/10 ml) is used with 3 mg of potassium oxalate for preserving blood.', 'role': 'assistant'}]