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: Pathology
[{'content': 'The cytoprotective agent used for the prevention of xerostomia in patients undergoing head and neck radiotherapy is \nSelect and explain. \nA. Valacyclovir, B. Amifostine, C. Glycopyrrolate, D. Naproxen', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]