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: Unknown
[{'content': 'Mc benign epithelial ovarian tumor is \nSelect and explain. \nA. Serous cystadenoma, B. Mucinous cystadenoma, C. Brenner tumor, D. Ovarian fibroma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Serous cystadenoma and cystadenocarcinoma\nSerous cystadenoma and cystadenocarcinoma are amongst the most common of cystic ovarian neoplasms, accounting about 50% of all ovarian tumours; of these, 60-70% are benign, 15% borderline and 20-25% are malignant.', 'role': 'assistant'}]