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: Forensic Medicine
Age of marriage of mentally retarded girl is: UP 09 
Select and explain. 
A. 16 years, B. 18 years, C. 21 years, D. Cannot marry
D: Cannot marry
Answer: D: Cannot marry 
Explanation: Ans. Cannot marry