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: Forensic Medicine
False but firm belief about something which is not a fact: WB 10; MP 11 
Select and explain. 
A. Illusion, B. Delusion, C. Hallucination, D. Obsession
B: Delusion
Answer: B: Delusion 
Explanation: Ans. Delusion