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: Psychiatry
All are features of autistic disorder except - 
Select and explain. 
A. Mental retardation, B. Absent social smile, C. Onset before 21/2 years, D. Third person hallucination
D: Third person hallucination
Answer: D: Third person hallucination 
Explanation: Mental retardation is seen in 50 - 75% of patients with autism.
There is the absence of social smile and eye to eye contact.
Onset is before 21/2 years.
Third person hallucination is characteristic of schizophrenia.