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
Preservation is: 
Select and explain. 
A. Persistent and inappropriate repetition of the same thoughts, B. When a patient feels very distressed about it, C. Characteristic of schizophrenia, D. Characteristic of obsessive compulsive disorder (OSD)
C: Characteristic of schizophrenia
Answer: C: Characteristic of schizophrenia 
Explanation: Characteristic of schizophrenia