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: Surgery
[{'content': 'A child with a history of pain over lower extremities since few moths shows radiological evidence of osteosarcoma. Most common site of osteosarcoma is: \nSelect and explain. \nA. Upper end of femur, B. Lower end of femur, C. Lower end of fibula, D. Lower end of tibia', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The classic form of osteosarcoma is typically seen in patients in their second or third decade, with a peak in the adolescent growth spu. It occurs more frequently in males than in females and is found in the metaphyseal areas of long bones, with 50% of lesions seen about the knee joint. The distal femur is the most common site, followed by the proximal tibia and then the proximal humerus. Ref: Randall R.L., Hoang B.H. (2006). Chapter 6. Musculoskeletal Oncology. In H.B. Skinner (Ed), CURRENT Diagnosis & Treatment in Ohopedics, 4e.', 'role': 'assistant'}]