This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
If iodine supplementation in the diet was completely stopped today, thyroid hormone levels in blood will fall to zero after: 
Select and explain. 
A. 7 days, B. 30 days, C. 90 days, D. 360 days
C: 90 days
Answer: C: 90 days 
Explanation: The thyroid gland has enough stores of iodine to sustain & to synthesize the thyroid hormone for 90 days even if there is no iodine supplementation.