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': 'An ideal imaging method for diagnosing hydro-cephalus in an infant is: \nSelect and explain. \nA. Plain X-ray, B. CT scan, C. Ultrasound, D. MRI', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Ultrasound', 'role': 'assistant'}]