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
[{'content': 'Which is the commonest malignancy of ovary? \nSelect and explain. \nA. Serous type, B. Mucinous type, C. Dermoid cyst, D. Granulosa cell tumor', 'role': 'user'}, {'content': "Answer: A \nExplanation: Serous cystadenoma and cystadenocarcinoma are amongst the most common of cystic ovarian neoplasm, accounting about 50% of all ovarian tumors, of these 60% are benign, 15% borderline and 25% are malignant. Of the all cystic tumors of the ovary 5 to 10% are dermoids. Dermoid cyst is usually unilocular, with smooth surface seldom attaining more than 15 cm in diameter. Granulosa cell tumours are fairly common and represents 10% of all solid ovarian tumours. Ref: Shaw's Textbook of Gynaecology, 13th Ed, Page 358-359.", 'role': 'assistant'}]