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': 'Grid is used: \nSelect and explain. \nA. To remove secondary radiation, B. Filter the radiation, C. Removes scattered radiation, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]