This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Pa of Basal ganglia, primarily involved in parkinsonism? 
Select and explain. 
A. Subthalamic nudes, B. Substantia nigra, C. Globus pallidus, D. None
B: Substantia nigra
Answer: B: Substantia nigra 
Explanation: Ans. is 'b' i.e., Substantia nigra