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': 'A metastatic tumour least common in - \nSelect and explain. \nA. Pelvis, B. Ribs, C. Small bone of lower limb, D. Vertebra', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The commonest sites for bone metastases are the vertebrae (commonest), pelvis, the proximal half of the femur, the humerus and ribs.\nExtremities distal to elbow and knee are least commonly involved sites.', 'role': 'assistant'}]