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': 'All of the following are components of developer except: \nSelect and explain. \nA. Developing agent, B. Activator, C. Restrainer, D. Hardener', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]