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: Radiology
[{'content': 'Ultrasound diagnoses all the following except \nSelect and explain. \nA. Anencephaly, B. Down syndrome, C. Placenta prae, D. * Hydatidiform mole', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Down syndrome', 'role': 'assistant'}]