This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Organic mental disorders, Subject name: Psychiatry
The characteristic symptom of organic psychosis is 
Select and explain. 
A. Hallucination, B. Depression, C. Transient delusion, D. Anxiety
A: Hallucination
Answer: A: Hallucination 
Explanation: All varieties of visual hallucination are found in acute organic states but small animals and insects are most often hallucinated in delirium. Reference: Fish's Clinical Psychopathology, page 23.