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': 'Role of fixer is: \nSelect and explain. \nA. It binds developer to film, B. It takes away extra developer solution, C. It strengthens/fixes the silver halides on to X-ray film, D. It removes the extra silver halides which are unfixed', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]