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': 'Setting reaction of solution liners: \nSelect and explain. \nA. Chemical reaction, B. Physical evaporation, C. Both of the above, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Solution Liners\nBased on non aqueous solution of acetone, alcohol or ether. Eg: Varnish (COPAL WASH).\nComposition:\n\n10% copal resin.\n90% solvent.\n\nSetting reaction: Physical evaporation.\n\nThin film; copal resin remains.\nSingle layer of varnish covers 55% of surface area.\nIf 2-3 layers are applied; 6-80% area is covered.', 'role': 'assistant'}]