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
Reversible cause of dementia -a) Hypothyroidismb) Alzheimer's diseasec) Vitamin B12 deficiencyd)  Vitamin A deficiency 
Select and explain. 
A. ac, B. bc, C. ad, D. b
A: ac
Answer: A: ac 
Explanation: None