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: Medicine
The single most powerful predictor of survival in multiple myeloma is - 
Select and explain. 
A. `M' component production, B. Bone marrwo plasmocytosis, C. Serum beta 2-microglobulin level, D. Serum calcium level
C: Serum beta 2-microglobulin level
Answer: C: Serum beta 2-microglobulin level 
Explanation: None