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': 'Presence of 1 up quark + 2 down quarks suggests the following: \nSelect and explain. \nA. Proton, B. Neutron, C. Electron, D. Positron', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]