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
Most common chromosomal syndrome is- 
Select and explain. 
A. Fragile X syndrome, B. Trisomy 17, C. Trisomy 21, D. Trisomy 13
C: Trisomy 21
Answer: C: Trisomy 21 
Explanation: Down syndrome or trisomy 21 is the most common chromosomal anomaly.