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: Surgery
Which is the most common cause of hypothyroidism 
Select and explain. 
A. Multinodular goiter, B. Lymphoma of thyroid, C. Autoimmune thyroiditis, D. Riedel's thyroiditis
C: Autoimmune thyroiditis
Answer: C: Autoimmune thyroiditis 
Explanation: None