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: Gynaecology & Obstetrics
A 25 year old female presents with a lower abdominal mass which shows a well-formed tooth on plain x-ray. The lesion is most likely to be which of the following? 
Select and explain. 
A. An immature teratoma, B. A dysgerminoma, C. An ovarian fibroma, D. A mature cystic teratoma
D: A mature cystic teratoma
Answer: D: A mature cystic teratoma 
Explanation: Well-formed teeth are commonly seen in mature cystic teratoma and not in any of the other lesions.