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': "Commonest ovarian tumour associated with pregnancy is : \nSelect and explain. \nA. Mucinous cystadenoma, B. Teratoma (Dermoid cyst), C. Brenner's tumour, D. Fibroma", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Teratoma (Dermoid cyst)', 'role': 'assistant'}]