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: Psychiatry
Most common cause of dementia is : 
Select and explain. 
A. Vitamin B12, B. Parkinsonism, C. Alzheimer's disease, D. Road traffic accidents
C: Alzheimer's disease
Answer: C: Alzheimer's disease 
Explanation: Alzheimer's disease is the most common cause of dementia.