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: Radiology
[{'content': 'What is the S.I. unit of effective dose? \nSelect and explain. \nA. Becquerel, B. Sievert, C. Gray, D. Roentgen', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The effective dose (E) is used to estimate the risk in humans. It is hard to compare the risk from a dental exposure with, for example, the risk from a radiographic chest examination because different tissues with different radiosensitivities are exposed.\xa0\nThe unit of effective dose is the Sv.', 'role': 'assistant'}]