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
A 60 year man had undergone cardiac bypass surgery 2 days back. Now he started forgetting things and was not able to recall names and phone numbers of his relatives. What is the probable diagnosis : 
Select and explain. 
A. Depression, B. Post traumatic psychosis, C. Cognitive dysfunction, D. Alzheimer's disease
C: Cognitive dysfunction
Answer: C: Cognitive dysfunction 
Explanation: The tendency to forget and inability to remember events immediately after cardiac bypass surgery suggests a diagnosis of cognitive dysfunction. Cognitive dysfunction present with impaired memory & intellect. Major surgery like prolonged cardiopulmonary bypass is one of the most consistent risk factors for cognitive dysfunction.