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
A 70-year-old man presents with h/o prosopagnosia, loss of memory, 3rd person hallucinations since 1 month. On examination deep tendon reflexes are increased, mini-mental examination score is 20/30. What is most likely diagnosis? 
Select and explain. 
A. Dissociative amnesia, B. Schizophrenia, C. Alzheimer's disease, D. Psychotic disorder
C: Alzheimer's disease
Answer: C: Alzheimer's disease 
Explanation: The presence of loss of memory, prosopagnosia (difficulty in identifying face) in a 70 year old man is quite suggestive of Alzheimer's disease. Third person auditory hallucinations are usually seen in schizophrenia; however they can be present in Alzheimer's disease too. Fuher on examination, deep tendon reflexes are increased, which again can be seen in late stage of Alzheimer's disease. Finally MMSE score below 24 seals the diagnosis.