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: Pharmacology
Which of the following inhibits rate limiting step of Norepinephrine synthesis 
Select and explain. 
A. Cocaine, B. Amphetamine, C. Metyrosine, D. Bretylium
C: Metyrosine
Answer: C: Metyrosine 
Explanation: Metyrosine inhibits tyrosine hydroxylase enzyme, which mediates the rate limiting step of norepinephrine synthesis (i.e conversion of Tyrosine to Dopa).