This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic Approach to Pediatric Medicine, Subject name: Pediatrics
Most common cause of Down's syndrome is - 
Select and explain. 
A. Monosomy 21, B. Trisomy 21, C. Robertsonian translocation, D. Mosaicism
B: Trisomy 21
Answer: B: Trisomy 21 
Explanation: Ans. is 'b' i.e., Trisomy 21 o Has been explained in previous sessions