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: Microbiology
Most common single cause of pyrexia of unknown origin 
Select and explain. 
A. Mycobacterium tuberculosis, B. Salmonella paratyphi, C. Brucella, D. Salmonella typhi
A: Mycobacterium tuberculosis
Answer: A: Mycobacterium tuberculosis 
Explanation: None