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 not a feature of 21st trisomy? \nSelect and explain. \nA. Mental retardation, B. Duodenal atresia, C. Hypeonicity, D. CHD', 'role': 'user'}, {'content': "Answer: C \nExplanation: Down's syndrome (21st trisomy) is the most common chromosomal disorder and a major cause of mental retardation. Children with Down's syndrome develop muscle hypotonia not hypeonia. Reference: Essential Paediatrics by O.P Ghai 6e page 592.", 'role': 'assistant'}]