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': 'Isotopes have same atomic: \nSelect and explain. \nA. Number, B. Number, C. Both weight and number, D. Density', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Number', 'role': 'assistant'}]