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: Pathology
Which is the most common primary malignant bone tumor? 
Select and explain. 
A. Osteosarcoma, B. Osteoclastoma, C. Secondaries, D. Multiple myeloma
D: Multiple myeloma
Answer: D: Multiple myeloma 
Explanation: Secondaries are the most common malignant bone tumor. But the most common primary malignant bone tumor is Multiple myeloma..