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 of the following finding on MR imaging distinguishes vaginal atresia from mullerian agenesis \nSelect and explain. \nA. Amount of upper vaginal dilatation, B. Presence of cervix, C. Length of atresia, D. Hymeneal ring', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Presence of cervix distinguishes vaginal atresia from mullerian agenesis.', 'role': 'assistant'}]