This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Heteopic calcification occurs in 
Select and explain. 
A. Ankylosing spondylitis, B. Rieter's syndrome, C. Forrestier'disease, D. Rheumatic ahritis
A: Ankylosing spondylitis
Answer: A: Ankylosing spondylitis 
Explanation: Ref, Robbins 7/e p41-2; Harrison 17/e p1952