question: Q:An investigator is studying a drug that acts on the thyroid hormone pathway. Levels of serum free T3 and T4 in healthy participants are measured before and after administration of the drug. After administration, there is a decrease in the average serum free T3 level, while the average serum free T4 level is increased compared to initial serum studies. Inhibition of which of the following is the most likely mechanism of action of this drug?? 
  {'A': 'Follicular thyroid proteases', 'B': 'Thyroid-stimulating hormone', 'C': 'Follicular iodotyrosine deiodinase', 'D': 'Follicular thyroid peroxidase', 'E': "Peripheral 5'-deiodinase"},