This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
A middle aged woman presented to the OPD with dull abdominal pain for 6 months. CT scan of pelvis showed a 7cm mass involving left ovary with irregular calcifications. The right fallopian tube & ovary are excised. What is the likely diagnosis? 
Select and explain. 
A. Mucinous cystadenoma, B. Choriocarcinoma, C. Dysgerminoma, D. Mature cystic teratoma
D: Mature cystic teratoma
Answer: D: Mature cystic teratoma 
Explanation: .