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': 'Thickness of stomach in ultrasound: \nSelect and explain. \nA. 2 mm, B. 5 mm, C. 7 mm, D. 10 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 5 mm', 'role': 'assistant'}]