This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basics of Psychiatry, Subject name: Psychiatry
A 24-year-old patient with schizophrenia tells the physician that he believes that CIA is listening to his telephone conversations through his television set. Despite being told multiple times by family members, he remains firm on his belief. This patient is describing 
Select and explain. 
A. a hallucination, B. an illusion, C. clouding of consciousness, D. delusion
D: delusion
Answer: D: delusion 
Explanation: A false belief, in this case that the CIA is listening to one's telephone conversations through the television set, is an example of a delusion. A hallucination is a false perception, and an illusion is a misperception of reality Clouding of consciousness is the inability to respond to external events