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
Late onset hemorrhagic cystitis after bone marrow transplanatation is caused by: 
Select and explain. 
A. Cyclophosphamide, B. Ifosfamide, C. Adeno virus, D. Cytomegalo virus
C: Adeno virus
Answer: C: Adeno virus 
Explanation: After bone marrow transplantation (BMT), early-onset hemorrhagic cystitis is related to drugs in the treatment regimen (e.g., cyclophosphamide, ifosfamide), and late-onset hemorrhagic cystitis is usually due to the polyoma virus BKV or adenovirus type 11. Ref: Harrisons principles of internal medicine, 18th edition, Page: 2275.