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
All of the following are causes pf pancytopenia with cellular bone marrow except - 
Select and explain. 
A. Paroxysomal noctural hemoglobinuria, B. Congential dyserythropoietic anemia, C. Megaloblastic anemia, D. Hairy cell leukemia
B: Congential dyserythropoietic anemia
Answer: B: Congential dyserythropoietic anemia 
Explanation: None