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: Unknown
Defense Mechanism which explains “compulsions” in a patient of obsessive compulsive disorder? 
Select and explain. 
A. Reaction formation, B. Regression, C. Undoing, D. Displacement
C: Undoing
Answer: C: Undoing 
Explanation: Undoing explains compulsions in patients of obsessive compulsive disorder