This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Rheumatoid Ahritis, Subject name: Medicine
[{'content': 'Earliest radiological change in RA: \nSelect and explain. \nA. Decreased joint space, B. Aicular erosion, C. Periaicular osteopenia, D. Subchondral cyst', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Radiological features of RA Evidence of soft tissue swelling and joint effusion Symmetrical involvement Juxta-aicular osteopenia (within weeks) Loss of aicular cailage and bone erosions (after months) Narrowing of joint space Aicular destruction and joint deformity, e.g. subluxation of atlantoaxial and cervical joints Lack of hyperophic bone changes (sclerosis or osteophyte)', 'role': 'assistant'}]