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
[{'content': 'In Alzheimer disease patients, the major effect on neurotransmitter systems of tacrine, donepezil, rivastigmine, and galantamine is to \nSelect and explain. \nA. increase dopamine availability, B. decrease dopamine availability, C. increase Ach availability, D. decrease Ach availability', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Low levels of Ach are associated with the symptoms of Alzheimer disease. Tacrine, donepezil, rivastigmine, and galantamine are acetylcholinesterase inhibitors (i.e., they block the breakdown of Ach, increasing its availability). These agents can thus be effective in slowing down the progression of the illness. They do not restore the function the patient has already lost.', 'role': 'assistant'}]