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': 'In order to prevent dehydration of periosteal surface of the flap, it should be irrigated frequently with: \nSelect and explain. \nA. Water, B. CHX, C. Saline, D. All of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: To prevent dehydration of periosteal surface of the ﬂap, it should be irrigated frequently with saline\xa0(0.9% NaCl), and not with water,\xa0as it is hypotonic.', 'role': 'assistant'}]