This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Symptoms & Signs , Subject name: Psychiatry
An 8 year old child after tonsillectomy sees a bear in her room. She screams in fright. A nurse who rushes in switches on the light, finds a rug wrapped on an armchair. She pacifies the child. What the child experienced was a: 
Select and explain. 
A. Delusion, B. Illusion, C. Hallucination, D. None of the above
B: Illusion
Answer: B: Illusion 
Explanation: B ref: Ahuja, 4th/e p. 13 and 5th/e p. 253