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
Mechanism of action of propylthiouracil in hyperthyroidism is: 
Select and explain. 
A. Inhibition of organification of iodine, B. Inhibition of oxidation of iodine, C. Inhibition of coupling of two DIT residues, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Propylthiouracil, carbimazole and methimazole act by inhibiting the enzyme, thyroid peroxidase. It catalyses:

Oxidation of iodine
Organification
Coupling