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': 'Silica sol: \nSelect and explain. \nA. Is applied to the walls of the investment to produce hygroscopic expansion, B. Increase the strength and the setting expansion of the phosphate-bonded investments, C. Acts as a retarder in the silica bonded investments, D. Acts as a refractory in the silica bonded investments', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]