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
Causes of thyrotoxicosis includes all of the following except: 
Select and explain. 
A. Grave's disease., B. Struma ovarii., C. Toxic adenoma., D. None.
D: None.
Answer: D: None. 
Explanation: None