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
Multiple myeloma is diagnosed by - 
Select and explain. 
A. 24 hours urine protein, B. Kidney biopsy, C. > 10% plasmacytosis, D. Rouleaux formation in blood
C: > 10% plasmacytosis
Answer: C: > 10% plasmacytosis 
Explanation: None