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
[{'content': "Crohn's disease may be caused by which one of the following infectious agents? \nSelect and explain. \nA. Clostridium difficle, B. Mycobacterium paratuberculosis, C. Cytomegalo virus (CMV), D. Mycoplasma", 'role': 'user'}, {'content': "Answer: A \nExplanation: A possible infectious etiology for IBD includes clostridium difficile, maparatuberculosis, paramyxovirus and helicobacter species, salmonella shigella, campylobacter species. M.para tuberculosis does not have a confirmed disease association and antimycobacterial agents are not effective in treating Crohn's disease. Ref: Harrison's Principles of Internal Medicine, 16th Edition, Pages 1176-78; Davidson's Principles and Practice of Medicine, 19th Edition, Page 808", 'role': 'assistant'}]