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: Medicine
[{'content': 'During treatment for Wilson disease with trientine and penicillamine, free serum copper should be kept below which level? \nSelect and explain. \nA. 25 mcg/dl, B. 50 mcg/dl, C. 75 mcg/dl, D. 100 mcg/dl', 'role': 'user'}, {'content': "Answer: A \nExplanation: The normal free copper value is 10-15 mcg/dL and it is often as high as 50 mcg/dL in untreated Wilson's disease. With treatment, free copper should be <25 mcg/dL. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 3190", 'role': 'assistant'}]