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: Gynaecology & Obstetrics
Trisomy 21 is also known as: September 2011 
Select and explain. 
A. Turner's syndrome, B. Klinefelter's syndrome, C. Down's syndrome, D. Alpo's syndrome
C: Down's syndrome
Answer: C: Down's syndrome 
Explanation: Ans. C: Down's syndrome