Final answer:
The diagnostic test that provides a definitive diagnosis of Alzheimer's disease is examination of the brain at autopsy.
Step-by-step explanation:
The diagnostic test that provides a definitive diagnosis of Alzheimer's disease is A) Examination of the brain at autopsy.
Autopsy is the only method that can definitively confirm the presence of Alzheimer's disease. During autopsy, the brain is examined for the accumulation of beta-amyloid plaques and neurofibrillary tangles, which are characteristic features of Alzheimer's disease.
Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) can provide valuable information about brain structure and function in patients suspected of having Alzheimer's disease, but they cannot provide a definitive diagnosis.