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
All of the following aEURoeCDaEUR markers used for diagnostic criteria for systemic mastocytosis EXCEPT 
Select and explain. 
A. CD, B. CD 25, C. CD 117, D. CD 20
D: CD 20
Answer: D: CD 20 
Explanation: . CD 20