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': 'A 26-year-old pregnant woman has been detected to have a diastolic murmur in mitral area. Echocardiography reveals mitral valve orifice to be 0.8 cm2. The cause of her murmur is \nSelect and explain. \nA. Mild mitral stenosis, B. Severe mitral stenosis, C. Functional murmur, D. Transmitted murmur from the congenital hea disease of the foetus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Severe mitral stenosis', 'role': 'assistant'}]