This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joint disorders, Subject name: Orthopaedics
Earliest investigation for diagnosis of Ankylosing spondylitis- 
Select and explain. 
A. MRI STIR sequence, B. Bone scan, C. CT scan, D. X-ray
A: MRI STIR sequence
Answer: A: MRI STIR sequence 
Explanation: mri stir sequence most precise investigation of choice in patients with ankylosing spondilitis ref : maheswari 9th ed