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
Which is not an ego defence mechanism : 
Select and explain. 
A. Rationalization, B. Repression, C. Identification, D. Obsession
D: Obsession
Answer: D: Obsession 
Explanation: D i.e Obsession