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': 'Multiple myeloma is diagnosed by - \nSelect and explain. \nA. 24 hours urine protein, B. Kidney biopsy, C. > 10% plasmacytosis, D. Rouleaux formation in blood', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]