Correct Answer :
C. Positron emission tomography scan
The major neuropathologic findings in Parkinson disease are a loss of pigmented dopaminergic neurons in the substantia nigra and the presence of Lewy bodies.
The characteristic symptoms of moderate Parkinson's disease can be remembered with the acronym TRAP:

Positron emission tomography (PET) and single photon emission CT (SPECT) are useful diagnostic imaging studies.
The scan uses 18-flurodopa to measure dopamine neurons in the substantia nigra area of the brain. The symptoms of Parkinsons are caused by loss of the dopamine neuron. 18-flurodopa is injected into the patient and then the brain is scanned. The scan is very sensitive to the dopamine cells and many people with Parkinsons will have an abnormal PET scan.
Magnetic resonance imaging (MRI) and computed tomography (CT) scan are unremarkable in Parkinson disease. No laboratory biomarkers exist for Parkinson disease. Serum ceruloplasmin concentration is obtained as a screening test for Wilson disease.