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: Radiology
Radioactive phosphorus is used in the treatment of – 
Select and explain. 
A. Polycythemia, B. Thyroid metastasis, C. Multiple myeloma, D. Embrynal cell carcinoma
A: Polycythemia
Answer: A: Polycythemia 
Explanation: Amongst the given options, Radioactive phosphorus has a well-established role in polycythemia vera. It has also been tried in multiple myeloma, however, its use for this is still debatable.