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: Pharmacology
[{'content': "The fastest acting antithyroid drug is: \nSelect and explain. \nA. Lugol's iodine, B. Radioactive iodine, C. Propylthiouracil, D. Sodium thiocyanate", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]