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: Pathology
True about struma ovarii -a) Ectopic thyroid tissueb) Ectopic ovarian tissuec) It is benignd) It is included in teratoma 
Select and explain. 
A. abc, B. ad, C. bc, D. acd
D: acd
Answer: D: acd 
Explanation: Struma ovarii is the presence of mature thyroid tissue as a major cellular component in an ovarian tumor.
Ovarian tumor is nearly always a teratoma.
Most of the tumors are benign and in some cases thyrotoxicosis develops.