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