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: Medicine
A middle aged female presents with polyarthritis with elevated rheumatoid factorANAanalevels, which among the following will help you to differentiate rheumatoid arthritis from SLE ? 
Select and explain. 
A. Soft tissue swelling at the proximal inter phalangial joint, B. Juxta articular osteoporosis or X-ray, C. Articular erosions on X-ray, D. Elevated ESR
C: Articular erosions on X-ray
Answer: C: Articular erosions on X-ray 
Explanation: None