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': "The earliest congenital malformation that can he detected on USG: \nSelect and explain. \nA. Anencephaly, B. Hydrocephalus, C. Sacral agenesis, D. Down's syndrome", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Anencephaly', 'role': 'assistant'}]