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
[{'content': 'The cell mass in multiple myeloma is formed by- \nSelect and explain. \nA. Circulating B cells settle in BM, B. Preformed B cells are seen in the marrow, C. Circulating B cells settle in BM, D. B-cells turn malignant and secrete light chains', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]