This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
All are chlolinergic agents except 
Select and explain. 
A. Galantamine, B. Donepezil, C. Tacrine, D. Memantine
D: Memantine
Answer: D: Memantine 
Explanation: Donepezil,rivastigmine,gallantamine and tacrine are cholinergic (due to inhibition of cholinesterase enzyme) drugs useful for alzheimer's disease. Memantine is an NMDA blocker,used for Alzheimer's disease. Ref-KDT 6/3 p472,473