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: Dental
[{'content': 'One bottle system of adhesive resins \nSelect and explain. \nA. 4th generation bonding agents, B. Separate etching step not required, C. Separate etching step is still required, D. Contains only primer', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]