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': 'The most radiosensitive tissue is: \nSelect and explain. \nA. Brain, B. Bone marrow, C. Thyroid, D. Liver', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Bone marrow', 'role': 'assistant'}]