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: Orthopaedics
[{'content': 'All of the following investigations are needed for the diagnosis of osteosarcoma, except - \nSelect and explain. \nA. MRI of femur, B. Bone marrow biopsy, C. Bone scan, D. CT chest', 'role': 'user'}, {'content': 'Answer: B \nExplanation: A biopsy of the lesion (not bone marrow biopsy) should always be carried out before commencing treatment.\nBone scan, MRI and CT chest are used.', 'role': 'assistant'}]