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
Hashimoto's disease is: 
Select and explain. 
A. Agranulomatous thyroiditis, B. An autoimmune thyroiditis, C. Fibrous thyroiditis, D. A viral infection of the thyroid gland
B: An autoimmune thyroiditis
Answer: B: An autoimmune thyroiditis 
Explanation: None