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': 'Stable matter is made up of: \nSelect and explain. \nA. Upquarks only., B. Downquarks only., C. Electrons., D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]