This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metastatic Tumors of Bone, Subject name: Orthopaedics
[{'content': 'Most common malignancy of bone is? \nSelect and explain. \nA. Secondary, B. Multiple myeloma, C. Osteoid osteoma, D. Osteosarcoma', 'role': 'user'}, {'content': "Answer: A \nExplanation: ANSWER: (A) secondaryREF: Apley's 8th edition page 191Most common malignancy of bone: secondariesMost common primary malignancy of bone: multiple myelomaMost common benign tumour of bone: osteochondromaMost common malignancy of bone in children and adolescents: osteosarcomaMost common benign true bone tumor: osteoid osteoma", 'role': 'assistant'}]