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': 'Ideal imaging modality to diagnose hydrocephalus in a one month old baby is: \nSelect and explain. \nA. Plain X-ray, B. Ultrasound, C. Computerised tomography, D. Magnetic Resonance Imaging', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Ultrasound', 'role': 'assistant'}]