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
[{'content': 'Struma ovarii is \nSelect and explain. \nA. Teratoma of ovary, B. Thyroid gland tumor in pregnancy, C. May present as hypothyroidism, D. Ovarian stromal hyperplasia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Struma ovarii is the most common type of specialised teratoma.\nIt is composed of mature thyroid tissue and may present as hyperthyroidism.', 'role': 'assistant'}]