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': 'It is normal response to orthodontic treatment for periodontal space to \nSelect and explain. \nA. Widen, B. Narrow, C. Shorten, D. Elongate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]