Which of the following is a treatment used for Alzheimer's disease?

Donepezil is an acetylcholinesterase inhibitor that is commonly used in the treatment of Alzheimer's disease. This medication works by increasing the levels of acetylcholine in the brain, a neurotransmitter important for learning and memory, which tends to decrease in people with Alzheimer's. By preventing the breakdown of acetylcholine, Donepezil helps to improve cognitive function and slow the progression of symptoms associated with Alzheimer's disease.

The other options listed do not have a primary indication for treating Alzheimer's disease. Ropinirole is primarily used for treating Parkinson's disease and restless legs syndrome. Topiramate is an anticonvulsant medication often used to treat epilepsy and prevent migraines. Diazepam is a benzodiazepine that is mainly used for anxiety disorders, muscle spasms, and seizures, but it is not indicated for the treatment of Alzheimer's. Thus, Donepezil is the appropriate choice for managing Alzheimer's symptoms.