This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth and development, Subject name: Pediatrics
[{'content': 'The most common chromosomal syndrome is _____ \nSelect and explain. \nA. Fragile-X-Syndrome, B. Trisomy 18, C. Trisomy 21, D. Trisomy 13', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Trisomy 21 (Down&;s syndrome) is the most common chromosomal syndrome. Chromosomal disorders: These may involve autosomal or sex chromosomes. Involving autosomes Involving sex Chromosomes Down&;s syndrome (Trisomy 21) Edward syndrome (Trisomy 18) Patau syndrome (Trisomy 13) Cri du chat syndrome (5p deletion) Klinefelter syndrome (47,XXY) Turner syndrome (45,XO) Ref: Nelson textbook of pediatrics 21st edition Pgno: 659', 'role': 'assistant'}]