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: Surgery
Specific for Ankylosing spondylitis is true? 
Select and explain. 
A. HLA, B. B27, C. Sacroileitis, D. Raised ESR
C: Sacroileitis
Answer: C: Sacroileitis 
Explanation: Answer- C. Sacroileitis