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': '______________ is not a property of X-rays \nSelect and explain. \nA. Ionization, B. Action on photographic film, C. Excitation, D. Collimation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]