This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bone Tumour, Subject name: Orthopaedics
[{'content': "Babu a 19-year-old male has a small circumscribed sclerotic swelling over diaphysis of femur; likely diagnosis is: \nSelect and explain. \nA. Osteoclastoma, B. Osteosarcoma, C. Ewing's sarcoma, D. Osteoid osteoma", 'role': 'user'}, {'content': 'Answer: D \nExplanation: (d) Osteoid osteoma- Well circumscribed sclerotic swelling over diaphysis of a long bone (femur) in a 19 years old suggests the diagnosis of osteoid osteoma.', 'role': 'assistant'}]