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: Pediatrics
[{'content': 'Which of the following is the earliest cardiac abnormality to develop in acute rheumatic fever? \nSelect and explain. \nA. MR, B. MS, C. AR, D. AS', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Acute rheumatic fever can cause mitral regurgitation, but stenosis develops decades later. Characterestic thickening of leaflets occurs with fibrous obliteration. There is also commissural fusion, chordal fusion, and shoening, and calcium deposition on the leaflets, chordae, and annulus.', 'role': 'assistant'}]