This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cognitive development and defence mechanism, Subject name: Psychiatry
Defence mechanism in OCD 
Select and explain. 
A. Progression, B. Regression, C. Magical thinking, D. Reaction formation
D: Reaction formation
Answer: D: Reaction formation 
Explanation: Three defense mechanisms are common in OCD- Isolation, Undoing & Reaction formation Isolation: Unconsciously isolate and disown their own thoughts, experiencing as forign thoughts. Undoing: unconsciously cancel out an unacceptable desire or act by performing another act. Reaction formation: suppress an unacceptable desire by taking on a lifestyle that expresses the opposite desire.