This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
Bacteria showing antigenic variation- 
Select and explain. 
A. Yersinia, B. Bordetella, C. Brucella, D. Borrelia
D: Borrelia
Answer: D: Borrelia 
Explanation: Borellia cause Relapsing fever Reason for relapse is antigenic variation by changing outer surface protein. Borellia readily undergoes antigenic variation reason for relapse