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': 'Band and loop space maintainer is: \nSelect and explain. \nA. Unilateral fixed non functional, B. Unilateral removable functional, C. Bilateral fixed non functional, D. Bilateral removable functional', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]