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: Pathology
Cause of essential (Primary) Hypertension is: 
Select and explain. 
A. Excessive sympathetic nervous system activity, B. Renal artery stenosis., C. Glomerulonephritis., D. Chronic Renal failure.
A: Excessive sympathetic nervous system activity
Answer: A: Excessive sympathetic nervous system activity 
Explanation: None