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 drug is corticosteroid synthesis inhibitor? 
Select and explain. 
A. Metyrapone, B. Finasteride, C. Flutamide, D. Mifepristone
A: Metyrapone
Answer: A: Metyrapone 
Explanation: Metyrapone inhibits 11 - β - hydroxylase enzyme and prevents synthesis of corticosteroids.