This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Musculoskeletal  disorders, Subject name: Pediatrics
[{'content': 'Most common rheumatic disease in children is ________ \nSelect and explain. \nA. Juvenile idiopathic ahritis, B. Juvenile ankylosing spondylitis, C. Systemic lupus erythematosus, D. Morphea', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The most common rheumatic disease in children is Juvenile idiopathic ahritis (JIA), Juvenile idiopathic ahritis represents a homogenous group of chronic disorders charcterized by Ahritis in >/= 1 joint Age at onset: <16 years Duration of disease: >/=6 weeks Ahritis is clinically defined as: Swelling or effusion, or the presence of 2 or more of the followin signs: Limitation of range of motion Tenderness or pain on motion Increased heat Ref: Nelson textbook of pediatrics 21st edition pgno: 1258', 'role': 'assistant'}]